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Use of js array filter() method

 Arrays are frequently used in development, and processing data in arrays is one of the more common and important operations. Therefore, processing data in arrays during development is an important skill. Every developer Everyone should master the operations of arrays, especially for junior developers who have just entered the industry, so be sure to master the relevant skills. This article mainly shares some operations to filter the data in the array, about the use of the filter() method.

The filter() method will not detect empty arrays and will not change the contents of the original array. The first parameter of this method is a callback function, and the second parameter is the object to be used as the callback to be executed. It is passed to the function and used as the value of "this". If thisValue is omitted, the value of "this" is "undefined", that is, if thisValue is omitted in strict mode, "this" is undefined; if thisValue is omitted in non-strict mode, "this" is window; if it is not omitted , "this" is the incoming object.

The following are some practical demonstration cases: The first is the basic use of the method.

       let arr=[1,2,3,4,5,6,7,8];
        let obj={
            id:'1001',
            name:"aaa",
        }
        let a= arr.filter(function(value,index,array){
            /* "use strict"
            console.log(this)//undefined */
            console.log(this);
            console.log(value,index,array);
            return value>2;
        },obj);
        console.log(a,Object.prototype.toString.call(a),a.length);
        console.log(arr);

Array deduplication

 let arr=[1,2,1,2,4,5];
        let a=arr.filter((value,index,array)=>{
            // return index===arr.indexOf(value);
            return index===array.indexOf(value);
        });
        console.log(a);// [1, 2, 4, 5]

Use with other methods

let arr=[1,2,3,4,5,6];
        let fun=function(num){
            if(num%2===0){
                return true;
            }
        }
        let a=arr.filter(fun);
        console.log(a);

Remove null items from an array

 let arr=[1,2,"null",null,"aaa",null];
        let a=arr.filter((value)=>{
            return value;
        })
        console.log(a)// [1, 2, "null", "aaa"]
        console.log(a)

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