String startswith in javascript

JavaScript String startsWith()

In JavaScript, the startsWith() method determines whether the given string begins with a specific sequence of characters. Let’s take a look at syntax and examples of the Javascript string startsWith() method.

Note: If you want to determine whether the given string ends with a specific sequence of characters then you can use JavaScript String endsWith()

startsWith() Syntax

The syntax of the startsWith() method is:

startsWith(searchString, position)

startsWith() Parameters

The startsWith() method takes two parameters.

• searchString (required): The characters that need to be searched at the start of the string.
• position (optional): The position of the string at which it needs to begin the search. It’s an optional parameter, and if the value is not specified, it defaults to position 0.

startsWith() Return Value

The startsWith() function returns true if the given characters are found at the beginning of the string. Otherwise, it returns false .

Note: The startsWith() method is case-sensitive.

JavaScript String startsWith() examples

In this example, you can notice that the startsWith() method is case-sensitive as the exact match returns true else returns false, as shown in the below code.

const text = 'Hello, Welcome to JavaScript World'; console.log(text.startsWith('Hello')); // true console.log(text.startsWith('hello')); // false

Since we have not given any position parameter, it will start from position 0 of the string.

JavaScript startsWith() example with Position parameter

If we do not specify the position parameter, the string search will begin from position 0, and if the string doesn’t match the given “searchString,” the method returns false, as shown below.

In the below example, we are searching Welcome, which is at position six, but since we have not specified the position parameter, it searches from the 0th position and does not match the search string and returns false.

const text = 'Hello, Welcome to JavaScript World'; console.log(text.startsWith('Welcome')); // false

Now, when we pass the exact position as a parameter where the string begins, the startsWith() method will begin the search from the specified position and match the string as shown in the below code.

const text = 'Hello, Welcome to JavaScript World'; console.log(text.startsWith('Welcome',6)); //true

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JavaScript String startsWith()

The startsWith() method returns true if a string starts with a specified string.

Otherwise it returns false .

The startsWith() method is case sensitive.

See Also:

Syntax

Parameters

Parameter	Description
searchValue	Required. The string to search for.
start	Optional. Start position. Default is 0.

Return Value

Type	Description
A boolean	Returns true if the string starts with the value. Otherwise it returns false .

Related Pages

Browser Support

startsWith() is an ECMAScript6 (ES6) feature.

ES6 (JavaScript 2015) is supported in all modern browsers:

Chrome	Edge	Firefox	Safari	Opera
Yes	Yes	Yes	Yes	Yes

startsWith() is not supported in Internet Explorer 11 (or earlier).

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String.prototype.startsWith()

The startsWith() method determines whether a string begins with the characters of a specified string, returning true or false as appropriate.

Try it

Syntax

startsWith(searchString) startsWith(searchString, position) 

Parameters

The characters to be searched for at the start of this string. Cannot be a regex. All values that are not regexes are coerced to strings, so omitting it or passing undefined causes startsWith() to search for the string «undefined» , which is rarely what you want.

The start position at which searchString is expected to be found (the index of searchString ‘s first character). Defaults to 0 .

Return value

true if the given characters are found at the beginning of the string, including when searchString is an empty string; otherwise, false .

Exceptions

Description

This method lets you determine whether or not a string begins with another string. This method is case-sensitive.

Examples

Using startsWith()

const str = "To be, or not to be, that is the question."; console.log(str.startsWith("To be")); // true console.log(str.startsWith("not to be")); // false console.log(str.startsWith("not to be", 10)); // true 

Specifications

Browser compatibility

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See also

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StartsWith() In JavaScript — How to check if a string starts with X?

In JavaScript, the easiest way to check if a string starts with something is to use the startsWith() function.

This article will tell you everything that you need to know about this function.

By the end of this guide, you will become a pro of this function and you will know:

1. How to use it?
2. When to use it?
3. And, will be able to explain it to others.

Definition

The startsWith() function is used to determine if a string begins by a search value.

If the string begins by the search value, it returns true , otherwise, it returns false .

javascriptconst str = "This is a very long string!"; // This will return true. ✅ console.log(str.startsWith('This')); // This will also return true. ✅ console.log(str.startsWith('This is a')); // This will return false. ❌ // startsWith() is case sensitive. console.log(str.startsWith('this')); // This will also return false. ❌ console.log(str.startsWith('string')); 

This is the startsWith() function syntax:

str.startsWith(searchValue[, startPosition]) 

Here are some things that you need to take into considerations:

Parameters

Parameters	Necessity	Description
searchValue	Required	The value to search for.
startPosition	Optional	The default position is 0, but you can specify your own.

Return Value

This method will return a boolean .

true => if the string starts with the search value.

false => if the string doesn’t start with the search value.

Browser Support

This method only works on browsers that support ES2015

Browser	Support
Chrome	YES ✅
Firefox	YES ✅
Opera	YES ✅
Safari	YES ✅
Edge	YES ✅
Internet Explorer	No ❌

To support legacy browsers like Internet Explorer you will need to add a polyfill.

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How to make the startsWith() function case insensitive?

To make the startsWith() function case insensitive you will need to make both the value and the searchValue lowercase.

javascriptconst str = "This is a very long string!".toLowerCase(); const searchValue = "THis".toLowerCase(); // This will return true. ✅ console.log(str.startsWith(searchValue)); 

Alternatively, you can use the regex method with the «i» modifier.

How to use the startsWith() function with multiple values?

When you need to check if a string starts with either of multiple values, you can check it in two ways.

javascriptconst str = "This is a very long string!"; // This will return true. ✅ console.log(str.startsWith('This') || str.startsWith('String')); 

javascriptconst str = "This is a very long string!"; // This will return true. ✅ console.log(['This', 'String'].some(word => str.startsWith(word))); 

How to fix » startsWith() is not a function»?

There are two main methods to fix this error.

1. You need to make sure that you are calling this function on a String. This method will only work on a String, so you will need to cast the value into a String.

javascriptconsole.log(String(unknownValue).startsWith("This")); 

1. You need to make sure your browser (or nodeJS) supports ES2015. If your environment doesn’t support the new EcmaScript you will need to use add this polyfill before calling the startsWith() function.

javascriptif (!String.prototype.startsWith) < String.prototype.startsWith = function (searchValue, position) < position = position || 0; return this.indexOf(searchValue, position) === position; >; > 

Are there alternatives to the startsWith() function?

Of course. There are a lot of alternatives to the startsWith() function.

You can use the indexOf() function, the substring function or a regex.

1. How to check if a string starts with another using indexOf() ?

You can get the same behavior as the startsWith() function by using the indexOf() function.

To replicate the startsWith() function, you will need to check if indexOf() return position is 0.

javascriptconst str = "This is a very long string!"; // This will return true. ✅ console.log(str.indexOf("This") === 0); // This will also return true. ✅ console.log(str.startsWith('This')); 

2. How to check if a string starts with another using substring() ?

You can check if a string starts with your search value by using the function substring with the length of the search value.

This method is a little more complicated.

javascriptconst str = "This is a very long string!"; // This will return true. ✅ console.log(str.substring(0, 4) === 'This'); // This will also return true. ✅ console.log(str.startsWith('This')); 

3. How to check if a string starts with another using a regex?

You can check if a string starts with your search value by using a regex.

This is pretty simple to do and you can specify the case sensitivity. To make the search case insensitive add the «i» modifier at the end of the regex.

javascriptconst str = "This is a very long string!"; // This will return true. ✅ const regex = /this/i; console.log(regex.test(str)); // This will also return true. ✅ console.log(str.startsWith('This')); 

Conclusion

Now that you are a pro of the startsWith() function in JavaScript, please share this article with others so they too can become a pro just like you.

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Hello! I am Tim Mouskhelichvili, a Freelance Developer & Consultant from Montreal, Canada. I specialize in React, Node.js & TypeScript application development. If you need help on a project, please reach out, and let’s work together.

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