Vanilla JavaScript string startsWith

A very nifty function in JavaScript is the startsWith() function. We can use this function to see if a string starts with a substring.

Javascript String startswith permalink

To use the function, we need to have a string. Then we can call the string.startsWith('substring') function and we will get a boolean value in return (true/false). The boolean confirms if the substring can be found at the beginning of the basestring.

const string =
  "Your time is limited, so don't waste it living someone else's life";

// Check if it starts with `Your time`
console.log(string.startsWith('Your time'));
// true

Important to know is that the startsWith method is case sensitive. So the following search string would return false:

const string =
  "Your time is limited, so don't waste it living someone else's life";

// Check if it starts with `your time`
console.log(string.startsWith('your time'));
// false

Using an offset search position on startsWith permalink

We now used the basic startsWith() function, but it accepts another parameter; the starting position. So let’s assume our string always starts with “Your time” but we want to see if the string after that is “is limited”. We can do so by offsetting the position.

const string =
  "Your time is limited, so don't waste it living someone else's life";

// Check if it starts with `is limited`
console.log(string.startsWith('is limited', 10));
// true

See the code examples in this Codepen permalink

Feel free to try the JavaScript code here:

See the Pen Vanilla JavaScript string startsWith by Chris Bongers (@rebelchris) on CodePen.

Browser Support permalink

This function works in all browsers but not in IE 😢. We can use this polyfill to help IE.

Thank you for reading, and let’s connect! permalink

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