Some basic explanations of JavaScript

The spread operator is represented by three dots. Its function is to expand an array or array-like object into a series of values ​​separated by commas. The spread operator has several functions. Let me explain them one by one! ! !

1, expand the array

//Expand the array let a = [1,2,3,4,5],b = [...a,6,7];console. log(b);//Printed value [1, 2, 3, 4, 5, 6, 7]

2, copy of the array

//Array Copy var c = [1, 2, 3]; var d = [...c]; d.push(4); console.log(d);//Printed value [1, 2, 3, 4 ]

3. Merging of arrays

//Merge of arrays var j = [7, 1, 2]; var k = [5, 0, 8]; j = [...k, ...j];console.log(j)//Printed value [5, 0, 8, 7, 1, 2]

Four, expand function Call

//Expand function call function fn(a,b,c,d){
console.log(a+b+c+d);}var p=[1,9, 3,,6];let result=fn(5,...p);Open function call //The printed value 18

The spread operator (spread) is three dots ( ...), converts an array||array-like||string into a comma-separated sequence. This guy is used to operate on arrays and take out all the things in the array

Extension operator

let zzz=[2,4,6];
console.log(zzz);//[2, 4, 6]
console.log(...zzz);//2 4 6

let a=[1,2,3];
let b=[...a,4,5,6];
console.log(b);//1,2,3,4,5,6

let [a,b,...c]=[1,2,3,4,5];
console.log(a,b);//1 2
console.log(c);//[3, 4, 5]

Arrow function

let say333=()=>{
    console.log("333");//333
}
say333();

(name)=>{
    console.log(name);
}

(a,b)=>{
    return a+b;
}

(a,b)=> a+b;

Parameter default value, remaining parameters , extended parameters

let aa=(name='wwrs')=>{
        console.log(`Hello ${name}`);
    }
    aa();//Hello wwrs
    aa('sss');//Hello sss
    
    
let bb=(a,b,c)=>{
        console.log(a+b+c);//9
    }
    let dd=[2,3,4];
    bb(...dd);
    
    
let he=(a,b,c,d)=>{
    console.log(a+b+c+d);//10
}
he(1,2,3,4)

let he1=(s,j,...shi)=>{
    console.log(shi);//[3, 4]
}
he1(1,2,3,4)

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