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 < 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 ! + ==?
This question is related to
javascript
syntax
logical-operators
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.)
!==
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'
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.
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'
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
Source: Stackoverflow.com