An overview of the

The find in js, findIndex indexof, includes can be used to find an item of the array, to compare the today. Test code address github.com/fanxuewen/e…

A, the find

Find returns undefined if the first item is found. This method does not change the original array. The usage is as follows

var findArr = [1, 2, 3, 4];
var res1 = findArr.find(item => {
    return item > 2;
})
var res2 = findArr.find(item => {
    return item > 10;
})
console.log('res1', res1);
console.log('res2', res2);
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var findArr1 = [1, , 3];
console.log('--------find---------');
var res1 = findArr1.find((item, index) => {
    console.log(item, The '-', index)
})
console.log('--------map---------');
findArr1.map((item, index) => {
    console.log(item, The '-', index);
})

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Second, the findIndex

FindIndex is used to find the first index that meets the criteria. If the index is found, the index is returned. If the index is not found, -1 is returned.

var findIndexArr = [1, 2, 3, 4];
var res1 = findIndexArr.findIndex(item => {
    return item > 2;
})
var res2 = findIndexArr.findIndex(item => {
    return item > 10;
})
console.log('res1', res1);
console.log('res2', res2);
//res1 2
//res2 -1
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Third, indexof

The indexOf() method returns the first index in the array where a given element can be found, or -1 if none exists. Syntax: arr.indexof (searchElement[, startIndex = 0]) startIndex indicates the starting position of the searchElement. Default: 0.

var indexOfArr = [1, 2, 3, 4]; Indexofarr.indexof (2) //1 indexofarr.indexof (2,2)//-1 indexofarr.indexof (9) //-1Copy the code

Four, includes

The includes() method is used to determine whether an array contains a specified value, returning true if it does and false otherwise.

    var includesArr = [1, 2, 3, 4];
    includesArr.indexOf(2)  //true
    includesArr.indexOf(9)  //false
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Five, the summary

Determine if there is an item in the array to use indexof/includes