Explain the meaning of the statement_html/css_WEB-ITnose

Array.prototype.i = Array.prototype.indexOf ||
function(value){
for (var i = this.length; i-- && this[i]!== value;) {}
return i;
};
What does this passage mean? ? Please explain.
Especially
Array.prototype.indexOf ||
function(value)
I don’t understand this!

Reply to the discussion (solution)

The indexOf in Array.prototype.indexOf is the method implemented by the class Array
which means:
If this method is implemented, this Array.prototype.i = Array.prototype.indexOf
That is, i and indexOf agree
If this method is not implemented, use the following function for the extension method i in Array Implement

Array.prototype.i = Array.prototype.indexOf || function(value) {    for (var i = this.length; i-- && this[i] !== value;) {}  //这里有点问题, return i;语句应该是在这个for循环体内的    return i;};//等价于if (Array.prototype.indexOf != false) Array.prototype.i;else Array.prototype.i = function(value) {	for (var i = this.length; i-- && this[i] !== value;) {		return i; 	}}

The function of the code is to add an i() method to the array type, check if the browser itself supports the indexOf method, and i will refer to the method (i becomes an alias of indexOf , if it is not supported, customize an i() method.
Array.indexOf() is supported by JS version 1.6, so it does not mean that all browsers support

such as
. b assignment, if a has a value, then assign the value of a to b, if a has no value, then assign 4 to b

			var a;			var b = a || 4;			alert(b)

is equivalent to
var a;
var b = a ? a : 4;
is equivalent to
var a;
if( a ){
b = a;
}else{
b = 4;
}

JScript code

Array.prototype.i = Array.prototype.indexOf || function(value) {
for (var i = this.length; i-- && ; this[i] !== value;) {} //There is a problem here, the return i; statement should be in the body of this for loop
return i...

like this , thank you all!