Javascript logical operator

Question

I am getting back into web development  and have been trying to go over the nuances of jscript recently  I was pouring through the source of the THREEx extension library built on top of Three JS and noticed this function  THREEx KeyboardState prototype pressed    function keyDesc        var keys      keyDesc split           for var i   0  i  lt  keys length  i             var key       keys i           var pressed          if  THREEx KeyboardState MODIFIERS indexOf  key       -1                pressed   this modifiers key            else if  Object keys THREEx KeyboardState ALIAS  indexOf  key      -1                pressed   this keyCodes  THREEx KeyboardState ALIAS key              else               pressed   this keyCodes key toUpperCase   charCodeAt 0                      if   pressed    return false             return true      I am looking in particular at the line here   if  THREEx KeyboardState MODIFIERS indexOf  key       -1      I am not familiar with this     operator  I checked w3schools and their logical operators list does not have this one included  I am not sure if this is misspelled and the browsers simply count it as    or if it has some other meaning  Also I was wondering whether this is actually a single logical operator or whether it is some kind of combination  like

User · Accepted Answer

You can find     and     operators in several other dynamically-typed languages as well  It always means that the two values are not only compared by their  implied  value  i e  either or both values might get converted to make them comparable   but also by their original type   That basically means that if 0     0  returns true  0      0  will return false because you are comparing a number and a string  Similarly  while 0     0  returns false  0      0  returns true

User · Answer

reference here      is the strict not equal operator and only returns a value of true if both the operands are not equal and or not of the same type  The following examples return a Boolean true    a     b  a      2   4      4

User · Answer

Copied from the formal specification  ECMAScript 5 1 section 11 9 5     11 9 4 The Strict Equals Operator              The production EqualityExpression   EqualityExpression     RelationalExpression is evaluated as follows          Let lref be the result of evaluating EqualityExpression    Let lval be GetValue lref     Let rref be the result of evaluating RelationalExpression    Let rval be GetValue rref     Return the result of performing the strict equality comparison rval     lval   See 11 9 6          11 9 5 The Strict Does-not-equal Operator              The production EqualityExpression   EqualityExpression     RelationalExpression is evaluated as follows          Let lref be the result of evaluating EqualityExpression    Let lval be GetValue lref     Let rref be the result of evaluating RelationalExpression    Let rval be GetValue rref     Let r be the result of performing strict equality comparison rval     lval   See 11 9 6    If r is true  return false  Otherwise  return true          11 9 6 The Strict Equality Comparison Algorithm      The comparison x     y  where x and y are values  produces true or false  Such a comparison is performed as follows          If Type x  is different from Type y   return false    Type x  is Undefined  return true    Type x  is Null  return true    Type x  is Number  then      If x is NaN  return false    If y is NaN  return false    If x is the same Number value as y  return true    If x is  0 and y is -0  return true    If x is -0 and y is  0  return true    Return false       If Type x  is String  then return true if x and y are exactly the same sequence of characters  same length and same characters in corresponding positions   otherwise  return false    If Type x  is Boolean  return true if x and y are both true or both false  otherwise  return false    Return true if x and y refer to the same object  Otherwise  return false

User · Answer

This is the strict not equal operator and only returns a value of true   if both the operands are not equal and or not of the same type  The   following examples return a Boolean true    a     b a      2  4      4

User · Answer

The     opererator tests whether values are not equal or not the same type  i e   var x   5  var y    5   var 1   y     x     true var 2   y    x     false

User · Answer

It s    without type coercion  See the MDN documentation for comparison operators   Also see this StackOverflow answer  which includes a quote from  JavaScript  The Good Parts  about the problems with    and      null    undefined  false     0   etc    Short answer  always use     and     unless you have a compelling reason to do otherwise   Tools like JSLint  JSHint  ESLint  etc  will give you this same advice

[javascript] Javascript logical "!==" operator?

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