What are the traversal methods of arrays in JS

1）forEach： It doesn't change the original array , no return value
Three parameters , Traversal value , Index value , The array itself

        var arr=[1,2,3,4,5,6]
        arr.forEach(item=>{
    
            console.log(item);
            // no return value 
            return item*2//undefined
        })

2）map： It doesn't change the original array , There is a return value
Parameters and forEach equally

        var arr=[1,2,3,4,5,6]
        const arrMap=arr.map(item=>{
    
            console.log(item);
            // no return value 
            return item*2
        })
        console.log(arrMap);//[2,4,6,8,10,12]

3）filter： Filter array , There is a return value , Returns an array of qualified elements , It doesn't change the original array
Parameters and forEach Agreement

        var arr=[1,2,3,4,5,6]
        const arrFilter=arr.filter(item=>{
    
            console.log(item);
            // no return value 
            return item<5
        })
        console.log(arrFilter);//[1,2,3,4]

4）for…of…： Returns the elements of the array , Property value of object , Can't traverse ordinary objects

        var arr =[1,2,3,4,5]
        for(let value of arr){
    
            console.log(value);// Return key value 
        }

5）reduce： Receive a function , As an accumulator , Do not change the original array
The function has four arguments , But two parameters are most commonly used , And must write , The first one returns the calculated value or initial value , The second is the current element

        var arr=[1,2,3,4]
        var arrReduce=arr.reduce((pre,item)=>{
    
            return pre+item
        },0)// here 0 Is the initial value of the first parameter 
        console.log(arrReduce);//10