Javascript String

JavaScript strings are primitive values. JavaScript strings are also immutable. It means that if you process a string, you will always get a new string. The original string doesn’t change. Strings are used for storing and manipulating text.

To create a string, you can use single quote or double quote.

let firstName = 'Folau';
let lastName = "Kaveinga";

String as objects

Don’t create strings as objects. It slows down execution speed and when it comes to comparison, it produces unexpected results.

let folau = new String("Folau");

let lisa = new String("Lisa");

let sameString = (folau=="Folau");// true
let sameObject = (folau==="Folau");// false

//When using the === operator, equal strings are not equal, because the === operator expects equality in both type and value.

var kinga = new String("kinga");             
var king = new String("kinga");

let samePerson = (kinga==king);// false, even though the value for both objects is "kinga"

To escape special characters, you use the backslash \ character.
if it’s a single quote string and you want to escape a single quote, you do this: \’
if it’s a double quote string and you want to escape a double quote, you do this: \”
if want to escape a backslash \, you do this: \\

let str = 'I\'m Folau Kaveinga.';
document.getElementById("userDesc").innerHTML = str;
let str1 = "I\"m Folau Kaveinga.";
let str2 = 'I\'m slash \\';

document.getElementById("userDesc").innerHTML += str1;
document.getElementById("userDesc").innerHTML += str2;

// output
I'm Folau Kaveinga.I"m Folau Kaveinga.I'm slash \

To get length of a string, you use the length function

let str = 'I\'m Folau Kaveinga.';

let strLength = str.length;
console.log("strLength: "+strLength); // strLength: 19

To access the characters in a string, you use the array-like [] notation with the zero-based index.

let name = "Folau Kaveinga";
let letter = name[4];
console.log("letter: "+letter);// u

To convert a non-string value to a string, use toString(), number + “”, or String(number)

let active = false;
let activeStr = active.toString(); 
console.log("activeStr: "+activeStr);// "false"

let five = 5;
let fiveStr = new String(five);
console.log("fiveStr: "+fiveStr);// 5

String concatenate

The concat() method concatenates one or more strings to another and returns the result string. Note that the concat() method does not modify the original string.

let firstName = 'Folau';
let fullName = firstName.concat(' ','Kaveinga', ' ', 'Jr');
console.log(fullName); // "Folau Kaveinga Jr"

You can also use the + operator to concatenate strings. In practice, the addition operator is used more often than the concate() method.

let firstName = 'Folau';
let fullName = firstName + ' '+ 'Kaveinga'+' '+'Jr';
console.log(fullName); // "Folau Kaveinga Jr"

To get a substring, use the substr or substring function

substr(startIndex,length);

The first argument startIndex the location at which the characters are being extracted, while the second argument length specifies the number of characters to extract.

substring(startIndex,endIndex)

Sometimes, you want to extract a substring from a string using starting and ending indexes.

let phrase = "I love coding";

console.log(phrase.substr(2, 4)); // "love"
console.log(phrase.substr(7, 6)); // "coding"
console.log(phrase.substring(7, 13)); // "coding"

To find position of a substring with a string, use the indexOf function

string.indexOf(substring,fromIndex);

You can also find the last index of a substring in a string by using the lastIndexOf function

string.lastIndexOf(substring,fromIndex)

let phrase = "I love coding so much";
console.log(phrase.indexOf("o")); // 3
console.log(phrase.indexOf('o', 3)); // 3
console.log(phrase.lastIndexOf('o')); // 15
console.log(phrase.indexOf('test'));// -1

The indexOf and lastIndexOf functions return -1 if substring is not found in the string.

There are more modern methods str.includes(substr, pos) returns true/false depending on whether str contains subtr within.

console.log( "Folau".includes("lau") ); // true
console.log( "Folau".includes("ol", 4 )); // false, from position 4 there is no "ol"

console.log( "Folau".startsWith("Fol") ); // true, "Folau" starts with "Fol"
console.log( "Folau".endsWith("lau") ); // true, "Folau" ends with "lau"

Remove leading and trailing whitespace, use trim(), trimStart(), and trimEnd()

let name = ' Folau ';
let strippedName= name.trim();
let leadingStrippedName= name.trimStart();
let trailingStrippedName= name.trimEnd();
console.log(strippedName); // "Folau"
console.log(leadingStrippedName); // "Folau "
console.log(trailingStrippedName); // " Folau"

Replace substring within a string, use replace function

string.replace(regularExpression, replaceText)

The first argument of the replace method could be a regular expression or a string. If it is a regular expression, the replace() method will find the matches and replace them with the second argument (replaceText). In case it is a string, the replace() method will perform an exact search and carry the replacement.

let phrase = "I love coding so much";
// replace "the" with "a"
let newPhrase = phrase.replace(/so/g, "very");
console.log(newPhrase); // "I love coding very much"
console.log(phrase); // "I love coding so much"

Source code on Github