JS implementation code to determine whether an element is within an array_javascript skills

1. JQuery

If you are using JQuery, you can use the inArray() function:

Detailed explanation of jquery inarray() function
jquery.inarray(value,array)
Determines the position of the first argument in the array (returns -1 if not found).

determine the index of the first parameter in the array (-1 if not found).
Return value
jquery
Parameters
value (any): used to find whether
exists in the array array (array): Array to be processed.

Usage:

Copy code The code is as follows:

$.inArray(value, array)

2. Write your own functions

function contains(arr, obj) {
  var i = arr.length;
  while (i--) {
    if (arr[i] === obj) {
      return true;
    }
  }
  return false;
}

Usage:

Copy code The code is as follows:

var arr = new Array(1, 2, 3);
contains(arr, 2);//return true
contains(arr, 4);//return false

3. Add a function to Array

Array.prototype.contains = function (obj) {
  var i = this.length;
  while (i--) {
    if (this[i] === obj) {
      return true;
    }
  }
  return false;
}

How to use:

Copy code The code is as follows:

[1, 2, 3].contains(2); //Return true
[1, 2, 3].contains('2'); //Return false

4. Use indexOf

But there is a problem that IndexOf is incompatible in some IE versions. You can use the following method:

if (!Array.indexOf) {
  Array.prototype.indexOf = function (obj) {
    for (var i = 0; i < this.length; i++) {
      if (this[i] == obj) {
        return i;
      }
    }
    return -1;
  }
}

First determine whether Array has an indexOf method, and if not, extend this method.

So the above code should be written before the code using the indexOf method:

var arr = new Array('1', '2', '3');
if (!Array.indexOf) {
  Array.prototype.indexOf = function (obj) {
    for (var i = 0; i < this.length; i++) {
      if (this[i] == obj) {
        return i;
      }
    }
    return -1;
  }
}
var index = arr.indexOf('1');//为index赋值为0