How to Parse Strings in JavaScript

Using String.split() method

The String.split() method in JavaScript is used to split a string into an array of substrings based on a specified separator, and returns the new array. For instance, if you have a string of “apple,banana,grape” and you want to separate each fruit into an array, you can do this by using the String.split(",") method.

let fruits = "apple,banana,grape";
let fruitsArray = fruits.split(",");
console.log(fruitsArray); // ["apple", "banana", "grape"]

How it works

The String.split() method divides a string into an ordered set of substrings, puts these substrings into an array, and returns the array. The division is done by searching for a pattern (specified separator) and separating the string whenever the pattern is found. If separator is an empty string, str is converted to an array of characters.

• The split() method is called on the string you want to divide.
• The character or characters you want to use as the split point are passed as an argument to the method.
• The method then goes through the string and every time it finds the character or characters it splits the string at that point.
• It returns the sections of the string as elements in an array.
• In our case, the string “apple,banana,grape” is split at each comma, resulting in the array [“apple”, “banana”, “grape”].

Using Regular Expressions with RegExp.exec() method

The RegExp.exec() method in JavaScript is a powerful tool that can be used to match a string against a regular expression and return an array of results. A better understanding of its working can be attained through a practical example.

var myRegEx = /(d+)/g;
var myString = "I have 100 apples and 200 oranges";
var result = myRegEx.exec(myString);

console.log(result);

How it works

The RegExp.exec() method executes a search for a match in a specified string and returns an array of information or null on a mismatch.

• The regular expression /(d+)/g is created, where d matches any digit (equivalent to [0-9]), + causes the engine to match the preceding character 1 or more times, and g is for global search (doesn’t return after the first match).
• A string, ‘I have 100 apples and 200 oranges’, is defined to be searched against the regular expression.
• The exec() method is used on the regular expression with the string as an argument, which returns an array of results.
• The array contains the matched strings along with their index positions and input strings. In this case, it contains ‘100’ from the position 7 and ‘200’ from the position 22.

Using String.indexOf() and String.substring() methods

We are going to use JavaScript’s String.indexOf() and String.substring() methods to locate a specific substring within a larger string and then extract it. For a better understanding, consider an example where we have a string “Hello, World!” and we want to extract “World” from it.

var str = "Hello, World!";
var index = str.indexOf("World");
var substring = str.substring(index, index + "World".length);

How it works

In the provided JavaScript code sample, we first locate the starting position of the target substring “World” in the source string “Hello, World!” using the indexOf() method. We then extract the substring starting from this position to the end of the target substring using the substring() method.

• Firstly, we define a string str = "Hello, World!".
• Then we use the indexOf() method on the string str to find the index at which the substring "World" begins. This will return the value 7, which is the position of "W" in the string str.
• We store this index in the variable index.
• Next, we use the substring() method on the string str to extract the substring that starts at the index found in the previous step and ends at the index representing the end of the substring we want to extract. This end index is calculated as index + "World".length.
• The string substring now holds the value “World”.