JavaScript does not mean what symbol

The inequality symbols of JavaScript include: 1. "!=" operator, used to compare whether the values ​​of two operands are not equal; 2. "!==" operator, used to compare two operands Check whether the values ​​of the operands are not equal and whether their types are not the same.

The operating environment of this tutorial: windows7 system, javascript version 1.8.5, Dell G3 computer.

javascript Not equal to operator

Not equal to operator	Description
!= (not equal)	Compare whether the values ​​of the two operands are not equal
!== (incomplete etc.)	Compare whether the values ​​of the two operands are not equal, and also detect whether their types are not the same

In the equality operation, the following should be noted A few questions:

• If the operand is a Boolean value, it is converted to a numerical value first, where false is converted to 0 and true is converted to 1.

• If one operand is a string and the other operand is a number, try to convert the string to a number first.

• If one operand is a string and the other operand is an object, try to convert the object to a string first.

• If one operand is a number and the other operand is an object, try to convert the object to a number first.

• If both operands are objects, the reference addresses are compared. If the reference addresses are the same, they are equal; otherwise they are not equal.

Example 1:

console.log("1" == 1);  //返回true。字符串被转换为数字
console.log(true == 1);  //返回true。true被转换为1
console.log(false == 0);  //返回true。false被转换为0
console.log(null != 0);  //返回true
console.log(undefined != 0);  //返回true
console.log(undefined == null);  //返回true
console.log(NaN != "NaN");  //返回true
console.log(NaN ==1);  //返回false
console.log(NaN == NaN);  //返回false
console.log(NaN != NaN);  //返回true

NaN is not equal to any value, including itself. The null and undefined values ​​are equal, but they are different types of data. In equality comparisons, null and undefined are not allowed to be converted to values ​​of other types.

Example 2:

Comparison of two objects. Although the structure is the same, the addresses are different, so they are not equal.

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

[Recommended learning: javascript advanced tutorial]

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