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How to forEach Over an Array in JavaScript

Topic: JavaScript / jQueryPrev|Next

Answer: Use the forEach() Method

You can simply use the array's forEach() method to loop through all the items in an array using JavaScript. The forEach() method executes a provided function once for each array element.

The following example will display all the values in the cities array using foreach loop.

  • <script>
  •     // Sample array
  •     var cities = ["London", "Paris", "New York", "Amsterdam"];
  •     
  •     // Loop over array
  •     cities.forEach(function(value){
  •         document.write("<p>" + value + "</p>");
  •     });
  • </script>

The forEach() method does not modify the original array (i.e. the array on which it is called). However, the callback function, if invoked, may do so. The following example will modify the given array by squaring each of its value (multiplying it by itself).

  • <script>
  •     // Sample array
  •     var numbers = [1, 2, 3, 4, 5, 6];
  •     
  •     // Loop over array and squaring each value
  •     numbers.forEach(function(value, index, array){
  •         array[index] = value * value;
  •     });
  •     
  •     console.log(numbers); // Prints: [1, 4, 9, 16, 25, 36]
  • </script>

The basic syntax of the forEach() method can be given with arr.forEach(function callback(value, index, array){ // your iterator }. The callback function is invoked with three arguments: the element value, the element index, and the array being traversed.

The forEach() was added to the ECMAScript standard in the 5th edition. This method is supported in all major modern browsers, such as Chrome, Firefox, IE9+, etc.


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