Javascript call apply vs bind

Question

I already know that apply and call are similar functions which setthis  context of a function    The difference is with the way we send the arguments  manual vs array   Question   But when should I use the  bind   method    var obj       x  81    getX  function         return this x          alert obj getX bind obj      alert obj getX call obj    alert obj getX apply obj      jsbin

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TL DR  In simple words  bind creates the function  call and apply executes the function whereas apply expects the parameters in array Full Explanation Assume we have multiplication function function multiplication a b   console log a b      Lets create some standard functions using bind var multiby2   multiplication bind this 2   Now multiby2 b  is equal to multiplication 2 b   multiby2 3     6 multiby2 4     8  What if I pass both the parameters in bind var getSixAlways   multiplication bind this 3 2    Now getSixAlways   is equal to multiplication 3 2   getSixAlways     6  even passing parameter returns 6  getSixAlways 12     6 var magicMultiplication   multiplication bind this    This create a new multiplication function and assigns it to magicMultiplication  Oh no  we are hiding the multiplication functionality into magicMultiplication  calling magicMultiplication returns a blank function b   on execution it works fine magicMultiplication 6 5     30 How about call and apply  magicMultiplication call this 3 2     6 magicMultiplication apply this  5 2      10

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Both Function prototype call   and Function prototype apply   call a function with a given this value  and return the return value of that function   Function prototype bind    on the other hand  creates a new function with a given this value  and returns that function without executing it   So  let s take a function that looks like this    var logProp   function prop        console log this prop         Now  let s take an object that looks like this    var Obj         x   5      y   10      We can bind our function to our object like this    Obj log   logProp bind Obj     Now  we can run Obj log anywhere in our code    Obj log  x       Output   5 Obj log  y       Output   10     Where it really gets interesting  is when you not only bind a value for this  but also for for its argument prop    Obj logX   logProp bind Obj   x    Obj logY   logProp bind Obj   y      We can now do this    Obj logX       Output   5 Obj logY       Output   10

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bind  It binds the function with provided value and context but it does not executes the function  To execute function you need to call the function   call  It executes the function with provided context and parameter   apply  It executes the function with provided context and  parameter as array

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call apply executes function immediately   func call context  arguments   func apply context   argument1 argument2         bind doesn t execute function immediately  but returns wrapped apply function  for later execution    function bind func  context        return function             return func apply context  arguments

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Here is one good article to illustrate the difference among bind    apply   and call    summarize it as below    bind   allows us to easily set which specific object will be bound to this when a function or method is invoked      This data variable is a global variable  var data          name  Samantha   age 12        name  Alexis   age 14    var user            local data variable      data                name  T  Woods   age 37            name  P  Mickelson   age 43             showData function  event            var randomNum     Math random      2   0    1  - 1     random number between 0 and 1          console log  this data randomNum  name         this data randomNum  age               Assign the showData method of the user object to a variable  var showDataVar   user showData  showDataVar        Samantha 12  from the global data array  not from the local data array      This happens because showDataVar    is executed as a global function and use of this inside  showDataVar    is bound to the global scope  which is the window object in browsers         Bind the showData method to the user object  var showDataVar   user showData bind  user      Now the we get the value from the user object because the this keyword is bound to the user object  showDataVar        P  Mickelson 43   bind   allow us to borrow methods     Here we have a cars object that does not have a method to print its data to the console  var cars         data           name  Honda Accord   age 14           name  Tesla Model S   age 2             We can borrow the showData    method from the user object we defined in the last example      Here we bind the user showData method to the cars object we just created   cars showData   user showData bind  cars   cars showData        Honda Accord 14    One problem with this example is that we are adding a new method showData on the cars object and  we might not want to do that just to borrow a method because the cars object might already have a property or method name showData  We don   t want to overwrite it accidentally  As we will see in our discussion of Apply and Call below   it is best to borrow a method using either the Apply or Call method  bind   allow us to curry a function  Function Currying  also known as partial function application  is the use of a function  that accept one or more arguments  that returns a new function with some of the arguments already set    function greet  gender  age  name           if a male  use Mr   else use Ms       var salutation   gender      male     Mr       Ms         if  age  gt  25            return  Hello      salutation   name             else           return  Hey      name                   We can use bind   to curry this greet function     So we are passing null because we are not using the  this  keyword in our greet function  var greetAnAdultMale   greet bind  null   male   45    greetAnAdultMale   John Hartlove        Hello  Mr  John Hartlove    var greetAYoungster   greet bind  null      16   greetAYoungster   Alex        Hey  Alex    greetAYoungster   Emma Waterloo        Hey  Emma Waterloo    apply   or call   to set this value  The apply  call  and bind methods are all used to set the this value when invoking a method  and they do it in slightly different ways to allow use direct control and versatility in our JavaScript code    The apply and call methods are almost identical when setting the this value except that you pass the function parameters to apply    as an array  while you have to list the parameters individually to pass them to the call    method    Here is one example to use call or apply to set this in the callback function      Define an object with some properties and a method     We will later pass the method as a callback function to another function  var clientData         id  094545      fullName   Not Set          setUserName is a method on the clientData object      setUserName  function  firstName  lastName                this refers to the fullName property in this object          this fullName   firstName         lastName            function getUserInput  firstName  lastName  callback  callbackObj            The use of the Apply method below will set the  this  value to callbackObj       callback apply  callbackObj   firstName  lastName          The clientData object will be used by the Apply method to set the  this  value  getUserInput   Barack    Obama   clientData setUserName  clientData      the fullName property on the clientData was correctly set  console log  clientData fullName      Barack Obama  Borrow functions with apply or call   Borrow Array methods  Let   s create an array-like object and borrow some array methods to operate on the our array-like object      An array-like object  note the non-negative integers used as keys  var anArrayLikeObj    0  Martin   1 78  2 67  3   Letta    Marieta    Pauline    length 4         Make a quick copy and save the results in a real array      First parameter sets the  this  value   var newArray   Array prototype slice call  anArrayLikeObj  0    console log  newArray        Martin   78  67  Array 3         Search for  Martin  in the array-like object   console log  Array prototype indexOf call  anArrayLikeObj   Martin       -1   false   true      true    Another common case is that convert arguments to array as following       We do not define the function with any parameters  yet we can get all the arguments passed to it   function doSomething          var args   Array prototype slice call  arguments       console log  args        doSomething   Water    Salt    Glue         Water    Salt    Glue    Borrow other methods  var gameController          scores    20  34  55  46  77        avgScore null       players               name  Tommy   playerID 987  age 23              name  Pau   playerID 87  age 33             var appController          scores    900  845  809  950        avgScore null       avg      function                   var sumOfScores   this scores reduce  function  prev  cur  index  array                      return prev   cur                        this avgScore   sumOfScores   this scores length                    Note that we are using the apply    method  so the 2nd argument has to be an array     appController avg apply  gameController      console log  gameController avgScore      46 4        appController avgScore is still null  it was not updated  only gameController avgScore was updated     console log  appController avgScore      null    Use apply   to execute variable-arity function   The Math max is one example of variable-arity function      We can pass any number of arguments to the Math max    method  console log  Math max  23  11  34  56       56   But what if we have an array of numbers to pass to Math max  We cannot do this   var allNumbers    23  11  34  56      We cannot pass an array of numbers to the the Math max method like this  console log  Math max  allNumbers       NaN   This is where the apply    method helps us execute variadic functions  Instead of the above  we have to pass the array of numbers using apply    thus   var allNumbers    23  11  34  56      Using the apply    method  we can pass the array of numbers  console log  Math max apply  null  allNumbers       56

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Syntax   call thisArg  arg1  arg2       apply thisArg  argsArray  bind thisArg   arg1   arg2             Here   thisArg is the object argArray is an array object arg1  arg2  arg3     are additional arguments    x000D   x000D  function printBye message1  message2   x000D      console log message1         this name        message2   x000D    x000D   x000D  var par01     name  John     x000D  var msgArray     Bye    Never come again       x000D   x000D  printBye call par01   Bye    Never come again       x000D    Bye John Never come again    x000D   x000D  printBye call par01  msgArray   x000D    Bye Never come again    John undefined x000D   x000D    so call   doesn t work with array and better with comma seperated parameters  x000D   x000D    printBye apply par01   Bye    Never come again        Error x000D   x000D  printBye apply par01  msgArray   x000D    Bye John Never come again    x000D   x000D  var func1   printBye bind par01   Bye    Never come again       x000D  func1     Bye John Never come again    x000D   x000D  var func2   printBye bind par01  msgArray   x000D  func2     Bye Never come again    John undefined x000D    so bind   doesn t work with array and better with comma seperated parameters x000D   x000D   x000D

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call    --  Here we pass the function arguments individually  not in an array format  var obj    name   Raushan     var greeting   function a b c        return  Welcome    this name     to    a         b     in     c      console log greeting call obj   USA    INDIA    ASIA       apply    --  Here we pass the function arguments in an array format  var obj    name   Raushan     var cal   function a b c        return this name    you got     a b c      var arr   1 2 3       array format for function arguments console log cal apply obj  arr       bind    --            var obj    name   Raushan            var cal   function a b c                return this name    you got     a b c                    var calc   cal bind obj          console log calc 2 3 4

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Call apply and bind  and how they are different   Lets learn call and apply using any daily terminology    You have three automobiles your scooter   your car and your jet which start with the same mechanism  method    We created an object automobile with a method push button engineStart    var your scooter  your car  your jet  var automobile             push button engineStart  function  runtime           console log this name     s      engine started  buckle up for the ride for     runtime     minutes              Lets understand when is call and apply used  Lets suppose that you are an engineer and you have your scooter  your car and your jet which did not come with a push button engine start and you wish to use a third party push button engineStart   If you run the following lines of code  they will give an error  WHY     your scooter push button engineStart      your car push button engineStart      your jet push button engineStart      automobile push button engineStart apply your scooter  20    automobile push button engineStart call your jet 10   automobile push button engineStart call your car 40     So the above example is successfully gives your scooter  your car  your jet a feature from automobile object   Let s dive deeper Here we will split the above line of code   automobile push button engineStart is helping us to get the method being used    Further we use apply or call using the dot notation   automobile push button engineStart apply    Now apply and call accept two parameters     context arguments   So here we set the context in the final line of code    automobile push button engineStart apply your scooter  20    Difference between call and apply is just that apply accepts parameters in the form of an array while call simply can accept a comma separated list of arguments    what is JS Bind function   A bind function is basically which binds the context of something and then stores it into a variable for execution at a later stage    Let s make our previous example even better  Earlier we used a method belonging to the automobile object and used it to equip your car  your jet and your scooter  Now lets imagine we want to give a separate push button engineStart separately to start our automobiles individually at any later stage of the execution we wish    var scooty engineStart   automobile push button engineStart bind your scooter   var car engineStart   automobile push button engineStart bind your car   var jet engineStart   automobile push button engineStart bind your jet     setTimeout scooty engineStart 5000 30   setTimeout car engineStart 10000 40   setTimeout jet engineStart 15000 5     still not satisfied   Let s make it clear as teardrop  Time to experiment  We will go back to call and apply function application and try storing the value of the function as a reference    The experiment below fails because call and apply are invoked immediately  hence  we never get to the stage of storing a reference in a variable which is where bind function steals the show  var test function   automobile push button engineStart apply your scooter

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It allows to set the value for this independent of how the function is called  This is very useful when working with callbacks     function sayHello        alert this message          var obj          message    hello         setTimeout sayHello bind obj   1000     To achieve the same result with call would look like this     function sayHello        alert this message          var obj          message    hello         setTimeout function   sayHello call obj    1000

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The main concept behind all this methods is Function burrowing   Function borrowing allows us to use the methods of one object on a different object without having to make a copy of that method and maintain it in two separate places  It is accomplished through the use of   call       apply     or   bind     all of which exist to explicitly set this on the method we are borrowing   Call invokes the function immediately and allows you to pass in arguments one by one  Apply invokes the function immediately and allows you to pass in arguments as an array  Bind returns a new function  and you can invoke call it anytime you want by invoking a function    Below is an example of all this methods  let name          firstname    Arham       lastname    Chowdhury     printFullName    function hometown company       console log this firstname         this lastname         hometown          company      CALL     the first argument e g name inside call method is always a reference   to  this  variable and latter will be function variable   printFullName call name  Mumbai   Taufa          Arham Chowdhury  Mumbai  Taufa   APPLY     apply method is same as the call method   the only diff is that  the function arguments are passed in Array list   printFullName apply name    Mumbai   Taufa           Arham Chowdhury  Mumbai  Taufa   BIND     bind method is same as call except that  the bind returns a function that can be used later by invoking it  does nt call it immediately    let printMyNAme   printFullName bind name  Mumbai   Taufa     printMyNAme           Arham Chowdhury  Mumbai  Taufa   printMyNAme   is the function which invokes the function  below is the link for jsfiddle  https   codepen io Arham11 pen vYNqExp

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Call  call invokes the function and allows you to pass arguments one by one  Apply  Apply invokes the function and allows you to pass arguments as an array  Bind  Bind returns a new function  allowing you to pass in a this array and any number of arguments    x000D   x000D  var person1    firstName   Raju   lastName   king    x000D  var person2    firstName   chandu   lastName   shekar    x000D   x000D  function greet greeting    x000D      console log greeting         this firstName         this lastName   x000D    x000D  function greet2 greeting    x000D          console log   Hello     this firstName         this lastName   x000D        x000D   x000D   x000D  greet call person1   Hello       Hello Raju king x000D  greet call person2   Hello       Hello chandu shekar x000D   x000D   x000D   x000D  greet apply person1    Hello        Hello Raju king x000D  greet apply person2    Hello        Hello chandu shekar x000D   x000D  var greetRaju   greet2 bind person1   x000D  var greetChandu   greet2 bind person2   x000D   x000D  greetRaju       Hello Raju king x000D  greetChandu       Hello chandu shekar x000D   x000D   x000D

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function sayHello                   alert this message               return this message            var obj                 message   Hello              function x country                var z   sayHello bind obj               setTimeout y   function w       this  reference not lost                     return z           country         w                 1000               return y            var t   x  India    World        document getElementById  demo   innerHTML   t

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I created this comparison between function objects  function calls  call apply and bind a while ago      bind allows you to set the this value now while allowing you to execute the function in the future  because it returns a new function object

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Use  bind   when you want that function to later be called with a certain context  useful in events  Use  call   or  apply   when you want to invoke the function immediately  and modify the context   Call apply call the function immediately  whereas bind returns a function that  when later executed  will have the correct context set for calling the original function  This way you can maintain context in async callbacks and events   I do this a lot   function MyObject element        this elm   element       element addEventListener  click   this onClick bind this   false       MyObject prototype onClick   function e         var t this     do something with  t           without bind the context of this function wouldn t be a MyObject       instance as you would normally expect       I use it extensively in Node js for async callbacks that I want to pass a member method for  but still want the context to be the instance that started the async action   A simple  naive implementation of bind would be like   Function prototype bind   function ctx        var fn   this      return function             fn apply ctx  arguments               There is more to it  like passing other args   but you can read more about it and see the real implementation on the MDN   Hope this helps

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Imagine  bind is not available   you can easily construct it as follow     var someFunction     var objToBind       var bindHelper    function  someFunction  objToBind        return function             someFunction apply  objToBind  arguments                bindHelper arguments

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Answer in SIMPLEST form    Call invokes the function and allows you to pass in arguments one by one   Apply invokes the function and allows you to pass in arguments as an array   Bind returns a new function  allowing you to pass in a this array and any number of arguments      Apply vs  Call vs  Bind Examples  Call  var person1    firstName   Jon   lastName   Kuperman    var person2    firstName   Kelly   lastName   King     function say greeting        console log greeting         this firstName         this lastName      say call person1   Hello       Hello Jon Kuperman say call person2   Hello       Hello Kelly King   Apply  var person1    firstName   Jon   lastName   Kuperman    var person2    firstName   Kelly   lastName   King     function say greeting        console log greeting         this firstName         this lastName      say apply person1    Hello        Hello Jon Kuperman say apply person2    Hello        Hello Kelly King   Bind  var person1    firstName   Jon   lastName   Kuperman    var person2    firstName   Kelly   lastName   King     function say         console log  Hello     this firstName         this lastName      var sayHelloJon   say bind person1   var sayHelloKelly   say bind person2    sayHelloJon       Hello Jon Kuperman sayHelloKelly       Hello Kelly King   When To Use Each  Call and apply are pretty interchangeable  Just decide whether it   s easier to send in an array or a comma separated list of arguments   I always remember which one is which by remembering that Call is for comma  separated list  and Apply is for Array   Bind is a bit different  It returns a new function  Call and Apply execute the current function immediately   Bind is great for a lot of things  We can use it to curry functions like in the above example  We can take a simple hello function and turn it into a helloJon or helloKelly  We can also use it for events like onClick where we don   t know when they   ll be fired but we know what context we want them to have   Reference  codeplanet io

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Use bind for future calls to the function  Both apply and call invoke the function  bind   also allows for additional arguments to be perpended to the args array  https   developer mozilla org en-US docs Web JavaScript Reference Global objects Function bind

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bind function should be use when we want to assign a function with particular context for eg   var demo                getValue   function                  console log  demo object get value       function                             setValue   function                    setTimeout this getValue bind this  1000                               in above example if we call demo setValue   function and pass this getValue function directly then it doesn t call demo setValue function directly because this in setTimeout refers to window object so  we need to pass demo object context to this getValue function using bind  it means we only passing function with the context of demo object not actully calling function   Hope u understand     for more information please refer  javascript bind function know in detail

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I think the same places of them are  all of them can change the this value of a function The differences of them are  the bind function will return a new function as a result  the call and apply methods will execute the function immediately  but apply can accept a array as params and it will parse the array separated And also  the bind function can be Currying

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They all attach this into function  or object  and the difference is in the function invocation  see below    call attaches this into function and executes the function immediately   var person         name   James Smith     hello  function thing        console log this name     says hello     thing          person hello  world        output   James Smith says hello world  person hello call   name   Jim Smith      world       output   Jim Smith says hello world    bind attaches this into function and it needs to be invoked separately like this   var person         name   James Smith     hello  function thing        console log this name     says hello     thing          person hello  world        output   James Smith says hello world  var helloFunc   person hello bind   name   Jim Smith      helloFunc  world        output  Jim Smith says hello world    or like this           var helloFunc   person hello bind   name   Jim Smith      world    helloFunc        output  Jim Smith says hello world    apply is similar to call except that it takes an array-like object instead of listing the arguments out one at a time   function personContainer       var person            name   James Smith        hello  function            console log this name     says hello     arguments 1                 person hello apply person  arguments     personContainer  world    mars       output   James Smith says hello mars   note  arguments 0     world    arguments 1     mars

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JavaScript Call    const person         name   Lokamn       dob  12      print  function  value value2            console log this dob value value2          const anotherPerson         name   Pappu        dob  12     person print call anotherPerson 1 2    JavaScript apply        name   Lokamn       dob  12      print  function  value value2            console log this dob value value2          const anotherPerson         name   Pappu        dob  12     person print apply anotherPerson  1 2       call and apply function are difference call take separate argument but apply take array  like  1 2 3      JavaScript bind        name   Lokamn       dob  12      anotherPerson            name   Pappu           dob  12          print2  function                  console log this                     var bindFunction   person anotherPerson print2 bind person   bindFunction

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The basic difference between Call  Apply and Bind are  Bind will be used if you want your execution context to come later in the picture  Ex  var car        registrationNumber   quot 007 quot     brand   quot Mercedes quot      displayDetails  function ownerName       console log ownerName     this is your car          this registrationNumber    quot   quot    this brand         car displayDetails  Nishant         Nishant this is your car 007 Mercedes    Let s say i want use this method in some other variable var car1   car displayDetails  Nishant    car1       undefined  To use the reference of car in some other variable you should use var car1   car displayDetails bind car   Nishant    car1       Nishant this is your car 007 Mercedes  Let s talk about more extensive use of bind function var func   function      console log this    bind 1    func       Number  1  Why  Because now func is bind with Number 1  if we don t use bind in that case it will point to Global Object  var func   function      console log this    bind       func       Object  Call  Apply are used when you want to execute the statement at the same time  var Name          work   quot SSE quot       age   quot 25 quot     function displayDetails ownerName        console log ownerName    quot   this is your name   quot     age    this age    quot   quot     work    this work     displayDetails call Name   Nishant      Nishant  this is your name  age25 workSSE     In apply we pass an array of arguments displayDetails apply Name    Nishant       Nishant  this is your name  age25 workSSE

[javascript] Javascript call() & apply() vs bind()?

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