Strings In-depth

Creating String

String Literals

Most of the time you will create string as literals.

let str = "Hello";

But, like an Array, you can create a string by using the String constructor.

let str = "Hello";
console.log(str);
console.log(typeof(str));

str = new String("Hello");
console.log(str);
console.log(typeof(str));

str = String("Hello");
console.log(str);
console.log(typeof(str));

It's interesting to look at the output of these three cases in the debugger. The second case shows an object with an internal array that has a length of 5. The other two cases return a literal string.

You can use the String constructor to convert a different type to a string. It doesn't work to convert an object, except for an array of primitive types.

str = String(500);
console.log(str); // 500

str = String(true);
console.log(str);  true

str = String([1,2,3]);
console.log(str);  // 1,2,3

str = String(["1", "2", "3"]);
console.log(str);  // 1,2,3

str = String({name: 'Jon'});
console.log(str); // [Object, Object]

Operators

Assignment

We learned in the introduction to the String object that you can concatenate string. We can also use the assignment operator to concatenate.

let output = "";
output+= "another thing";
output+= " and one more";
console.log(output); // another thing and one more.

Comparison

You can compare two strings, based on their ascii codes.

console.log("a" < "b");  // true

Conversion

let str = new String(true);
console.log(str); // "true"

Methods

Here are a few example. There are more, but the are all pretty straight forward to use and easy to look up so I'll just link to the documentation.

String - JavaScript | MDNMDN Web Docs

Splitting a string into an array

let str = "this is a string";
let array = str.split(" ");
console.log(array); // ["this", "is", "a", "string"];

Finding the Index Of a sub string in a string

Returns the index of the first occurrence of the sub string in the string. If the sub string cannot be found, -1 will be returned.

You can pass the start index as the second parameter.

let str = "this is a string";
let index = str.indexOf("is");
console.log(index); // 2

index = str.indexOf("is", 3);
console.log(index); // 5

Return a section of the string

let str = "this is a string";
let substr = str.substring(0, 6);
console.log(substr); // this i

let email = '[e-mail]';
let domain = email.substring(email.indexOf('@') + 1);

console.log(domain); // gmail.com