js other operators

(?:) is a ternary operator

(?:) is similar to if and can be used as a shortcut for if...else statements

condition? result 1: result 2; here you write the condition in front of a question mark (?) followed by result 1 and result 2 separated by a colon (:). Result 1 if the condition is met otherwise result 2

var b='gf';

(b == 'gf') ? a="true" : a="false";

console.log(a);

output ----------------------------- true

var b=true;

(b == false) ? a="true" : a="false";

console.log(a);

output ----------------------------- false

typeof

typeof can be used to detect the data type of a given variable, possible return values: 1. 'undefined' --- this value is undefined;

2. 'boolean' --- the value is a boolean;

3. 'string' --- the value is a string;

4. 'number' --- this value is a numerical value;

5. 'object' --- the value is an object or null;

6. 'function' --- This value is a function.

var aa = 'my name is gaofan';   

           console.log(typeof aa);    

           console.log(typeof 6);  

output // string
     // number

delete

delete is a unary operator that deletes object properties or array elements

var num = {x :1,y:2,k:3};
delete num.x;
    console.log(JSON.stringify(num))

输出{"y":2,"k":3}

var num = [1,2,3];
delete num[2]; // delete the last element of the array
    console.log(JSON.stringify(num))

output [1,2,null]

Delete the array, the length of the array has changed, the length of the array is still 3

viod() is a unary operator, the operand can be any data type, and the result of the calculation is ignored and returns undefined

<a href="javascript:void window.open();">Open a new window</a>

eval() has only one parameter. If the parameter passed in is not a string, he returns this parameter directly. If the parameter is a string, he will compile the string as js code.

function a(){
 eval("var x=1");
 console.log(x);
}
a();
console.log(x);
/* The first console.log() function can pop up 1 and the second will report an error because x is not defined
The eval() function does not create a new scope, and its scope is the scope it is in */

Global eval() can declare or change variables

var globalEval = eval; //Define the global eval function alias
var a = 'global' //global variable
function c(){
  var a = 'jimi,'; //local variable
eval('a+="gaofan"'); //Directly change the value of local variables
 return a; //return the changed local variable
}
console.log(c());            //localchanged

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