A brief discussion on JavaScript iteration method_Basic knowledge

The five iteration methods all accept two parameters: the function to be run on each item and the scope in which to run the function (optional)

every(): Runs the given function on each item in the array. Returns true if the function returns true for each item.
Filter(): Runs the given function on each item in the array. Returns an array of items that this function will return true.
forEach(): Runs the given function on each item in the array. This function has no return value.
Map(): Runs the given function on each item in the array. Returns a function consisting of the results of each function call.
Some(): Runs the given function on each item in the array. If the function returns true for any item, then return true

Copy code The code is as follows:

var numbers = [1, 2, 3, 4, 5, 4, 3, 2, 1];
​​​​ //every() and some() are most similar
//every() item: current traversed item, index: current item index, array: array object itself
      var everyResult = numbers.every(function (item, index, array) {
               return item > 2;
        });
alert(everyResult);//false
           //some()
      var someResult = numbers.some(function (item, index, array) {
               return item > 2;
        });
alert(someResult);//true
           //filter
        var filterResult = numbers.filter(function (item, index, array) {
               return item > 2;
        });
alert(filterResult);//[3,4,5,4,3]
​​​​ //map()
        var mapResult = numbers.map(function (item, index, array) {
              return (item * 2);
        });
alert(mapResult);//[2,4,6,8,10,8,6,4,2]
​​​​ //forEach is essentially the same as the for loop
      var forEachResult=numbers.forEach(function(item,index,array){
alert(item)
        });

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