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The indexOf () method of 1.javascript

Var arr_data= [1,2,3]

Arr_data.indexOf (1); / / if there is a subscript for the return value, there is no return-1

The $.inArray () method of 2.jquery

$.inArray (1, arr_data); / / if there is a subscript for the return value, there is no return-1

3.arr.find ()

The find () of the array instance is used to find the first qualified array element. Its argument is a callback function, and all array elements iterate through the callback function in turn until the first element with a return value of true is found, and then it is returned, otherwise undefined is returned.

Note: find () is not executed for empty arrays. Find () does not change the original value of the array

Arr.find (function (value) {

If (the value that value=== is looking for) {

/ / then include the element

})

Const myArr= [1,2,3,4,5,6]

Var v=myArr.find (value= > value > 4)

Console.log (v); / / the existing value returns the element

Var v=myArr.find (value= > value > 10)

Console.lof (v); / / does not exist. Return undefined

The callback function takes three parameters. Value: the current array element. Index: the current index value. Arr: the array to be found

Var arry= [23,34,43,4,41,45,6]

Var v=arry.find ((value,index,arr) = > {

Return index==4

})

Console.log (v); / / 41 returns the element

4.arr.findIndex () returns the position of the first qualified array element, or-1 if all elements do not match the condition.

Note: find (), findIndex () make up for the deficiency of index: (that is, judging NAN)

[NaN] .indexOf (NaN) / /-1

[NaN] .findIndex (y = > Object.is (NaN, y)) / / 0

Var arry= [23,34,43,4,45,45,6]

Var i=arry.findIndex ((value) = > value==4)

Console.log (I); if it exists, returns the position of the element in the array, here it returns 3, and if it doesn't exist, it returns-1.

5.for cycle and if judgment

Var arr= [1, 5, 10, 15]

/ / traditional for

For (let item0; I

If (ARR [I] = lookup value) {

/ / then include the element

}

}

/ / for...of

For (v of arr) {

If (vested values = lookup value) {

/ / then include the element

}

}

/ / forEach

Arr.forEach (v = > {

If (vested values = lookup value) {

/ / then include the element

}

})

Filter ()

Filter () is also used in the same way as find (). Also receive three parameters. The difference is in the return value. Filter () returns an array of all the elements that satisfy the condition, while find () returns only the first element that meets the condition. If the condition is not met, filter () returns an empty array, while find () returns undefined

Var arry= [23,34,43,4,41,23,34,45,6]

Console.log (arry.filter (item= > item > 40)); / / [43,41,45] returns an array that meets the criteria

Array deduplication

Console.log (arry.filter ((value,index,arr) = > arry.indexOf (value) = index)); / / [23, 34, 43, 4, 41, 45, 6]

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