What are the special operators in javascript

Javascript special operators include: 1. The comma operator "," can return the value of the rightmost operand; 2. The "delete" operator deletes an attribute of an object; 3. " in" operator; 4. "instanceof" operator; 5. "typeof" operator; 6. "void" operator.

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

1. Comma operator: Returns the value of the rightmost operand

The comma operator in JavaScript is a binary operator. It executes the operand on the left first, then the operand on the right, and finally returns the value of the operand on the right.

a = b = 1,c = 2;

console.log(a); //返回1

console.log(b); //返回1

console.log(c); //返回2

var x = (1, 2, 3);
alert(x);  //3

2. Delete operator: delete an attribute of an object

The delete operator is to delete an attribute from an object property, or remove an element from an array.

var obj = {x: 1, y: 2};
obj.x;  //1
delete obj.x;
obj.x;  //undefined

Note:

1. delete cannot delete the properties of an object whose configurable label is false:

var obj = {};
Object.defineProperty(obj, 'x', {
    configurable: false,
    value: 1
});
delete obj.x;  // false
obj.x;  // 1

2. It cannot be used to delete constants

var a = 1;
delete a;  // false

3. Cannot be used to delete function declarations

function fun() {}
delete fun;  // false

3.<span style="font-size: 18px;">"in"</span> Operator: Determine whether an attribute belongs to an object

The in operator requires that the operand on the left is a string and the operand on the right is an array or object , if the value on the left is a property name of the object on the right, it returns true, otherwise it returns false.

var obj = {
	name: 'person',
	age: 20
};
'name' in obj;  // true

4. instanceof operator

The instanceof operator requires that the operand on the left is an object and the operand on the right is an object class The name of the operator returns true if the object on the left side of the operator is an instance of the class on the right side of
, otherwise it returns false.

var d = new Date();

d instanceof Date; //返回true

d instanceof Object; //返回true

d instanceof Number; //返回false

5. typeof operator

typeof is a unary operator, placed before an operand, the operand can be anything Type of. Its return value is a string that describes the type of the operand. Usually the type returned by typeof is as follows: number, string, boolean, object, function, undefined

typeof can enclose the operand, Similar to the usage of a function

var today=new Date();

typeof myFun //返回object

typeof shape //返回string

typeof size //返回number

6. void operator

void is a unary operator, which can appear in any type of operand Before. This operator has a special purpose. It always discards the
value of the operand and returns undefined. This operator is commonly used in client-side javascript: URLs, where the value of an expression can be calculated without the browser displaying the value. Another use of void is to specifically generate undefined values ​​

var a = b = c = 2;  
d = void (a -= (b *= (c += 5))); 

console.log(a);  //返回-12

console.log(b);  //返回14

console.log(c);  //返回7

console.log(d);  //返回undefined

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