Using JavaScript to Convert String to Integer

We can use JavaScript to convert a string to an integer by using the JavaScript parseInt() method.

var num = parseInt("20.12345");

The above code would return the number 20.

The parseInt() JavaScript method will parse the value given to it as a string and then return the first Integer in the string. If no integer is found at the start, NaN will be returned.

Some other examples of the parseInt() method are below:

var num1 = parseInt("$11");
var num2 = parseInt("30 40 50");
var num3 = parseInt("The first number is 2 followed by 3");
var num4 = parseInt("10.10 is the first number");
var num5 = parseInt("-10 50");

console.log(num1);
console.log(num2);
console.log(num3);
console.log(num4);
console.log(num5);

#Output
NaN
30
NaN
10
-10

Note the parseInt() JavaScript method is similar to the parseFloat() method, the main difference being that parseInt() will only return the Integer, while parseFloat() will return decimal values as well.

Convert String to Integer using JavaScript

Below we will provide code to let the user input a string, and then use the parseInt() method to return the first Integer. Here is our simple HTML setup:

<p>Type something you want to use the parseInt() method on below:</p>
<input id="userVal" type="text" value="">
<div id="click-me"  onclick="convertStringToInt()">Convert to Integer</div>
<div id="results"></div>

Below is the JavaScript code which takes the user input using an onclick event, and uses the parseInt() method on that user input. We update the results below using the textContent property.

function convertStringToInt(){
  document.getElementById("results").textContent = parseInt(document.getElementById("userVal").value);
};

The final code and output for this example is below:

Code Output:

Full Code:

<p>Type something you want to use the parseInt() method on below:</p>
<input id="userVal" type="text" value="">
<div id="click-me"  onclick="convertStringToInt()">Convert to Integer</div>
<div id="results"></div>

<script>

function convertStringToInt(){
  document.getElementById("results").textContent = parseInt(document.getElementById("userVal").value);
};

</script>

Hopefully this article has been useful in helping you understand how to use JavaScript to convert a string to int.