How to get the first n values of an array in JavaScript?

Javascript Web Development Front End Technology

In this article we are going to discuss how to get the first n values of an array using JavaScript.

First, n value − to find the elements from the first index to n (n is the given number or given index) suppose you have given the n value as 5 the returned elements will be from index 0 to 5.

Using the _.first() function

To get the first n elements of an array we have many logical methods. But underscore.js provides the _.first() function. Which will directly or in a simple way gives the output.

Note − if we did not mention the n value in the _.first() function then it will be returned as the first element of an array. Following is the syntax of the _.first() function −

_.first(array,n)

It takes the array and a number as a parameter so, it will give the first n value from the array and returns the first n elements of an array as output.

Example: 1

In the following example, we are passing an integer array in _.first() function −

<!DOCTYPE html>
<html>
<head>
   <script src="https://cdnjs.cloudflare.com/ajax/libs/underscore.js/1.9.1/underscore-min.js"></script>
</head>
<body>
   <script type="text/javascript">
      var array = [1, 2, 3, 4, 5, 6, 7];
      document.write(_.first(array, 4));
   </script>
</body>
</html>

Example 2

Let us see another example for this −

<!DOCTYPE html>
<html lang="en">
<head>
   <meta charset="UTF-8" />
   <meta http-equiv="X-UA-Compatible" content="IE=edge" />
   <meta name="viewport" content="width=device-width, initial-scale=1.0" />
   <title>Get the first n values from an array</title>
   <script src="//cdnjs.cloudflare.com/ajax/libs/lodash.js/0.10.0/lodash.min.js"></script>
   <div id="first"></div>
</head>
<body>
   <script>
      let arr = new Array("Alice", 40, "Edward", "Cullen");
      let n = 2;
      document.getElementById("first").innerHTML =
      "First n elements from an array is : " + _.first(arr, n);
   </script>
</body>
</html>

Using the slice() method

Using the slice method you can get the elements in the selected range in the new array the syntax of the slice() method is −

arr.slice(0,n);

Example 1

The following example demonstrates to get first n elements of an array using the slice() method in JavaScript.

<!DOCTYPE html>
<html lang="en">
   <head>
   <meta charset="UTF-8" />
   <meta http-equiv="X-UA-Compatible" content="IE=edge" />
   <meta name="viewport" content="width=device-width, initial-scale=1.0" />
   <title>Get the first n values from an array</title>
   <div id="slice"></div>
</head>
<body>
   <script>
      let arr = new Array("Alice", 40, "Edward", "Cullen");
      let n = 2;
      let firstN = arr.slice(0, n);
      document.getElementById("slice").innerHTML ="First n elements from an array is : " + firstN;
   </script>
</body>
</html>

Example 2

In the following example, the slice() method in JavaScript is used to get first n elements of an array.

<!DOCTYPE html>
<html lang="en">
<head>
   <meta charset="UTF-8" />
   <meta http-equiv="X-UA-Compatible" content="IE=edge" />
   <meta name="viewport" content="width=device-width, initial-scale=1.0" />
   <title>Get the first n values from an array</title>
   <div id="slice"></div>
</head>
<body>
   <script>
      let n = 3;
      let getFirstN = function (...arr) {
         let sliceArr = arr.slice(0, n);
         return sliceArr;
      };
      document.getElementById("slice").innerHTML =
      "First n elements from an array is : " +
      getFirstN("Alice", 40, "Edward", "Cullen");
</script>
</body>
</html>