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This article mainly introduces javascript identity operator which is introduced in the text is very detailed, has a certain reference value, interested friends must read!

In javascript, the identity operator is "===," which compares the operands on both sides of an equation for equality. "===" In comparison operations, not only are the values of two operands compared for equality, but they are also checked for the same type; if the values are equal and the type is the same, true is returned.

Operating environment of this tutorial: Windows 7 system, Javascript version 1.8.5, Dell G3 computer.

In javascript, the identity operator is "===," which compares the operands on both sides of an equation for equality.

The "===" operator not only compares the values of two operands for equality, but also detects whether they are of the same type.

In identity operations, the following issues should be noted:

If both operands are simple values, they are congruent as long as the values are equal and of the same type.

If one operand is a simple value and the other operand is a compound object, it is not congruent.

If both operands are compound objects, the reference addresses are compared for the same.

(1) If the type is different, it must not be equal.

(2) If both are numerical values and are the same value, then they are equal; if at least one of them is NaN, then they are not equal. (To determine whether a value is NaN, you can only use isNaN( ) to determine)

(3) If both are strings and the characters at each position are the same, then they are equal, otherwise they are not equal.

If both values are true or false, then they are equal.

(5) If both values refer to the same object or function, then they are equal, otherwise they are not equal.

If both values are null or undefined, then they are equal.

Examples 1

Here are congruent comparisons of special operands.

console.log(null === undefined); //returns falseconsole.log(0 === "0"); //returns falseconsole.log(0 === false); //returns false

Example 2

Here is a comparison of two objects that return true because they both reference the same address.

var a = {};var b = a;console.log(a === b); //returns true

Although the following two objects have the same structure, they have different addresses, so they are not exactly equal.

var a = {};var b = {};console.log(a === b); //returns false

Example 3

For composite objects, the comparison focuses on referenced addresses, not on object values.

var a = new String("abcd"); //Defines the string "abcd" object var b = new String("abcd"); //Defines the string "abcd" object console.log (a === b); //Returns falseconsole.log (a == b); //Returns false

In the example above, the two objects have equal values but different reference addresses, so they neither want to wait nor are they exactly equal. Therefore, for compound objects, the results of the equality == and congruence == operations are the same.

Example 4

For simple values, as long as they are of the same type and equal in value, they are congruent, regardless of the process change of expression operation, and regardless of the reference address of variables.

var a = "1" + 1;var b = "11";console.log(a ===b); //returns true

Example 5

Expression (a>b|| A==b) is not exactly equal to the expression (a>=b).

var a = 1;var b = 2;console.log((a > b ||a == b) == (a >= b); //returns true, which seems equal

If null and undefined are assigned to variables a and b, respectively, the return value is false, indicating that the two expressions are not exactly equivalent.

var a = null;var b = undefined;console.log((a > b ||a == b) == (a >= b)); //Returns false, expression values are not equal

Because null == undefined equals true, the expression (a > b)|| A == b) returns true, but the expression null >= undefined returns false.

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