How to determine if an element is in an array in javascript

Method: 1. Use the indexOf() function to get the position where the specified element first appears in the array. If the return value is "-1", the element is not in the array; 2. Use lastIndexOf() to get the specified element. The position of the last occurrence of the element in the array. If the return value is "-1" the element is not in the array.

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

In javascript, you can use the indexOf() and lastIndexOf() functions to determine whether the element is in the array. The

indexOf() and lastIndexOf() methods can retrieve array elements and return the index position of the specified element; if the specified element does not exist, "-1" is returned.

Use indexOf() to find elements in the array

indexOf() returns the first match of an element value in the array The index, or -1 if the specified value is not found. The usage is as follows:

array.indexOf(item,start)

• item Required. The element to find.

• #start Optional integer parameter. Specifies the position in the array to start searching. Its legal values ​​are 0 to stringObject.length - 1. If this parameter is omitted, the search will start from the first character of the string. The

#indexOf() method performs a search in ascending index order, that is, retrieval from left to right. When retrieving, the array elements will be compared congruently with the searchElement parameter value ===.

Example: Find whether an element is in an array

var arr = ["ab","cd","ef","ab","cd"];
var str="cd";
if(arr.indexOf(str)===-1){
	console.log("指定元素："+str+" 不在数组中");
}else{
	console.log("指定元素： "+str+" 在数组中");
}

##Modify the value you need to find:

var str="gh";
if(arr.indexOf(str)===-1){
	console.log("指定元素："+str+" 不在数组中");
}else{
	console.log("指定元素： "+str+" 在数组中");
}

Use lastIndexOf() to find elements in the array

indexOf() returns the last 1 of an element value in the array The index of a match, or -1 if the specified value is not found. Its usage is the same as indexOf().

Example: Find whether an element is in an array

var arr = ["ab","cd","ef","ab","cd"];
var str="gx";
if(arr.lastIndexOf(str)===-1){
	console.log("指定元素："+str+" 不在数组中");
}else{
	console.log("指定元素： "+str+" 在数组中");
}

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