Convert a string to number in Javascript

Javascript is not a strongly type casted language. And it is very closely coupled to the browser DOM. So, now and then we end up parsing UI components like headings and paragraphs that contain a mix of strings and numbers.

In this article, I am going to describe how to convert a string to number in Javascript.

Convert a string to number in Javascript

We can use parseInt() function to convert a string to number in Javascript. The parseInt() function takes 2 parameters. The first parameter should be a string and the second parameter must be the base. We are talking about decimal point numbers here, so the base will be 10 in our case.

See the below example.

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let str = '100 dollars';
let num = parseInt(str, 10);
console.log(num);  // 100

This method can’t convert string to floating-point numbers.

For example, the below code will print the integer part of the number.

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let str = '14.5 dollars';
let num = parseInt(str, 10);
console.log(num);  // 14

Convert string to a floating-point integer

We can use parseFloat() method to convert string to a floating-point number. This method takes only one parameter which should be a string.

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let str = '14.50 dollars';
let num = parseFloat(str, 10);
console.log(num);  // 14.5

But I’m not sure if the number is integer or floating-point

In such cases, we can use the Number() function. It takes only one parameter which should be a string. Please see below example for details.

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let str = '14.50 dollars';
console.log( Number(str )); // 14.5 
let str2 = '100dollars';
console.log( Number(str2 )); // 100

Important Note:

The above examples will work only with a string that starts with a number. For example '123abc'.

But what if the number is not at the beginning of the string?

Then all of the above-mentioned methods will return a "NaN".

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let str = 'abc123';
parseInt(str); // NaN
parseFloat(str); // NaN
Number(str); // NaN

Extract a number from any position of a string

We can use a regex match() method to extract a number from any position of a string. The match() method returns an array as a result.

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let str = 'abc123';
let extract = str.match(/\d+$/);
console.log(extract[0]); // "123"

In this case, we have to access the 0th index of the array to get the result.

But, what if the string contains multiple numbers.

For example:

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let str = 'a20bc123';
 let extract = str.match(/\d+$/);
 console.log(extract[0]); // "20"

This will return the first match, which is 20 in this case.

Extract multiple numbers from different positions of a string

To extract multiple numbers, we have to make a little change in the regex.

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str = 'adasd10dsds105';
var matches = str.match(/\d+/g);
console.log(matches); // ["10", "105"]

The match function returns a string array, so we might need a further conversion of these results based upon the intended use.