Detailed explanation of new features of JavaScript_ECMA5 array

var arr = [ 1, 2, 3, 4, 5, 4, 3, 2, 1 ];

Method to add new position: indexOf lastIndexOf

1.1 parameters indicate the value to be passed back to the index position (index starts from 0)

var index = arr.indexOf(4);

alert(index); //3

2. When there are 2 parameters, the first parameter indicates the starting position. The second parameter or the value.

var index = arr.indexOf(4,4);

alert(index); //5

3. When they look for array comparisons '==='

lastIndexOf

var index = arr.lastIndexOf(2);

alert(index); //7

5 new iteration methods

1.every: Run a function for each element of the array. If true is returned, it will return true. If there is a return false, it will return false.

 var result = arr.every(function(item , index , array){ return item >= 1 ; });alert(result); //true

2.filter: Run a function for each element of the array. The given function is executed to return the filtered result.

 var result = arr.filter(function(item , index , array){return item > 2 ;});alert(result); //3,4,5,4,3

3.forEach: Loop the value of each item in the array and execute a method

 arr.forEach(function(item, index, array){ alert(item); //1,2,3,4,5,4,3,2,1});

4.map Run a function for each element of the array and can return the new result after the function is executed.

 var result = arr.map(function(item, index, array){ return item*10;});alert(result); //10,20,30,40,50,40,30,20,10

5.some: Run a function for each element of the array. If there is an item that returns true, it will return true. If each item returns false, it will return false.

 var result = arr.some(function(item, index, array){ return item >5 ;});alert(result); //false

reduce reduceRight

The starting position of the variable is different

Previous value, current value, index position, array

 var result = arr.reduce(function(prev , cur , index , array){ return prev + cur ;});alert(result) //25;var result = arr.reduceRight(function(prev , cur , index , array){ return prev + cur ;});alert(result) //25;

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