Replace a value if null or undefined in JavaScript

Question

I have a requirement to apply the    C  operator to JavaScript and I don t know how  Consider this in C    int i  null  int j i    10   j is now 10   Now I have this set up in JavaScript   var options          filters             firstName  abc                   var filter options filters 0        should get  abc  here  it doesn t happen var filter2 options filters 1        should get empty string here  because there is only one filter   How do I do it correctly   Thanks   EDIT  I spotted half of the problem  I can t use the  indexer  notation to objects  my object 0    Is there a way to bypass it   I don t know the names of the filters properties beforehand and don t want to iterate over them

User · Accepted Answer

Here   s the JavaScript equivalent   var i   null  var j   i    10    j is now 10   Note that the logical operator    does not return a boolean value but the first value that can be converted to true   Additionally use an array of objects instead of one single object   var options         filters                          name   firstName               value   abc                     var filter    options filters 0             is  name  firstName   value  abc   var filter2   options filters 1             is      That can be accessed by index

User · Answer

should be preferred to    because it checks only for nulls and undefined  All The expressions below are true   null     x        x     undefined     x        x      Most of the times you don t want the result below         x        x      0     x        x     false     x        x      -----    Using    is preferred  null     x        x     undefined     x        x         works only for null and undefined  which is in general safer         x             0     x       0    false     x       false     Bottom line  int j i    10  is perfectly fine to use in javascript also  Just replace int with let  Asterisk  Check browser compatibility and if you really need to support these other browsers use babel

User · Answer

Logical nullish assignment  2020  solution A new operator has been added       This is equivalent to value   value    defaultValue      and  amp  amp   are similar  links below  This checks if left side is undefined or null  short-circuiting if already defined  If not  the left side is assigned the right-side value  Basic Examples let a             undefined let b   null let c   false  a     true     true b     true     true c     true     false     Equivalent to a   a    true  Object Array Examples let x     quot foo quot   let y     foo   quot fizz quot     x 0       quot bar quot       quot foo quot  x 1       quot bar quot       quot bar quot   y foo      quot buzz quot       quot fizz quot  y bar      quot buzz quot       quot buzz quot   x     Array    quot foo quot    quot bar quot    y     Object   foo   quot fizz quot   bar   quot buzz quot     Functional Example function config options        options duration     100     options speed     25     return options    config   duration  555           duration  555  speed  25   config                           duration  100  speed  25   config   duration  null          duration  100  speed  25        Browser Support Nov 2020 - 77      Mozilla Documentation     Mozilla Documentation  amp  amp   Mozilla Documentation

User · Answer

I spotted half of the problem  I can t use the  indexer  notation to objects  my object 0    Is there a way to bypass it    No  an object literal  as the name implies  is an object  and not an array  so you cannot simply retrieve a property based on an index  since there is no specific order of their properties  The only way to retrieve their values is by using the specific name   var someVar   options filters firstName    Returns  abc    Or by iterating over them using the for     in loop   for var p in options filters        var someVar   options filters p     Returns the property being iterated

User · Answer

ES2020 Answer   The new Nullish Coalescing Operator  is finally available on JavaScript  though browser support is limited  According to the data from caniuse  only 48 34  of browsers are supported  as of April 2020    According to the documentation       The nullish coalescing operator      is a logical operator that   returns its right-hand side operand when its left-hand side operand is   null or undefined  and otherwise returns its left-hand side operand    const options     filters       firstName  abc          const filter   options filters 0         const filter2   options filters 1           This will ensure that both of your variables will have a fallback value of    if filters 0  or filters 1  are null  or undefined    Do take note that the nullish coalescing operator does not return the default value for other types of falsy value such as 0 and     If you wish to account for all falsy values  you should be using the OR operator

User · Answer

Destructuring solution Question content may have changed  so I ll try to answer thoroughly  Destructuring allows you to pull values out of anything with properties  You can also define default values when null undefined and name aliases  const options         filters             firstName    quot abc quot            const  filters   firstName    quot John quot   lastName    quot Smith quot      options     firstName    quot abc quot     lastName    quot Smith quot    NOTE  Capitalization matters  If working with an array  here is how you do it  In this case  name is extracted from each object in the array  and given its own alias  Since the object might not exist      was also added  const options         filters             name   quot abc quot           value   quot lots quot            const  filters   name   filter1    quot John quot          name   filter2    quot Smith quot            options     filter1    quot abc quot     filter2    quot Smith quot   More Detailed Tutorial Browser Support 92  July 2020

[javascript] Replace a value if null or undefined in JavaScript

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