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In JavaScript , in which cases the following statements won't be logically equal ?
if(x){}
and
if(x==true){}
Thanks
855
Javascript is like Java in that the == operator compares the values of primitive types, but the references of objects. You're creating two arrays, and the == operator is telling you that they do not point to the same exact object in memory: var b = new Array( 1, 2, 3 ); var c = new Array( 1, 2, 3 ); console.
An alternative approach is to use the logical OR (||) operator. To check if a value is of boolean type, check if the value is equal to false or equal to true , e.g. if (variable === true || variable === false) .
Use the strict equality (===) operator to check if a variable is equal to true - myVar === true . The strict equality operator will return true if the variable is equal to true , otherwise it will return false . Copied!
if you use if x ,it means it has to evaluate x for its truth value. But when you use x ==True or x is True . It means checking whether type(x)==bool and whether x is True. attention : x is True is no equal to bool(x)==True.
They are not at all equal.
if (x)
checks if x is Truthy where as the later checks if the Boolean value of x is true.
For example,
var x = {};
if (x) {
console.log("Truthy");
}
if (x == true) {
console.log("Equal to true");
}
Not only an object, any string (except an empty string), any number (except 0 (because 0 is Falsy) and 1) will be considered as Truthy, but they will not be equal to true.
As per ECMA 5.1 Standards, in if (x), Truthiness of x will be decided, as per the following table
+-----------------------------------------------------------------------+
| Argument Type | Result |
|:--------------|------------------------------------------------------:|
| Undefined | false |
|---------------|-------------------------------------------------------|
| Null | false |
|---------------|-------------------------------------------------------|
| Boolean | The result equals the input argument (no conversion). |
|---------------|-------------------------------------------------------|
| Number | The result is false if the argument is +0, −0, or NaN;|
| | otherwise the result is true. |
|---------------|-------------------------------------------------------|
| String | The result is false if the argument is the empty |
| | String (its length is zero); otherwise the result is |
| | true. |
|---------------|-------------------------------------------------------|
| Object | true |
+-----------------------------------------------------------------------+
Note: The last line object, which includes both objects and Arrays.
But in the later case, as per The Abstract Equality Comparison Algorithm,
If Type(x) is Boolean, return the result of the comparison ToNumber(x) == y.
If Type(y) is Boolean, return the result of the comparison x == ToNumber(y).
value of x will be converted to a number and that number will be checked against true.
Note:
In JavaScript, true is 1 and false is 0.
console.log(1 == true);
# true
console.log(0 == false);
# true
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