Javascript - String

String literal

String literal: A single quote ' or a double quote “ indicate string values.

var myVariable = 'Foo';
// is equivalent to
var myVariable = "Foo" ;

String Object

var myVariable = String(var);

Template literal (heredoc)

• Template literals

var myString = `hello!
 world!`;

Generate / Repeat

• Repeat

"string".repeat(10)

• or Array join

Array(11).join("a")

Concat

"my string" + "my string"
"35" + "25"

Replace

Replace uses generally a regular expression as first parameter.

// Not 
var regexp = '/pattern/md'
// but
var regexp = /pattern/md

Example: Suppress comments lines

text = "// My beautiful comment\r\nmy beautiful code\r\n";
text = text.replace(/^[/]{2}[^\r\n]+[\r\n]+/mg, "");
console.log(text);

where:

• The regexp pattern can be read as:
  • have no quotes but two slashes / as enclosing character.
  • ^ - the start of the pattern
  • [/]{2}: two backslashs
  • [^\r\n]: All characters excepts the end of line \r\n. The ^ character is a negation in a class.
  • + is a quantifier meaning one or more
  • mg are modifier that says respectively 'm': multiline matching, 'g': global match (find all matches rather than stopping after the first match)

match

match ¹⁾ uses generally a regular expression as first parameter.

The result returns:

• an array of matches (depend on the g flag)
• or null if no matches are found.

Example:

let result =  "blue is beautiful".match(/bl*/m);
console.log(result);

// Not 
var regexp = '/pattern/md'
// but
var regexp = /pattern/md

Contains / Includes

²⁾

var s = "HelloWorld";
if ( s.includes("Hello") ) {
   console.log("Hello You !");
}
console.log(`Does the string contains Hello: ${s.includes("Hello")}`);
console.log(`Does the string contains foo: ${s.includes("Foo")}`);

ReplaceAll

To replace all the character in a string, you need to add mg to the pattern of replace

Example: Replace all x with a y:

text = "xxxxxxxxxxxxxxxxxxxxxxxx";
text = text.replace(/x/mg, "y");
console.log(text);

Length

s = "length";
console.log(s.length);

charCodeAt

charCodeAt return code units rather than code points.

s = "Hello Foo";
console.log("The string ("+s+") is made of character coded with one code units and has then a length of "+s.length);
console.log("First code unit of "+s+" is "+s.charCodeAt(0));

s= "𐌰";
console.log("The character "+s+" is encoded with two code units and has then a length of "+s.length);
console.log("First code unit of "+s+" is "+s.charCodeAt(0));
console.log("Second code unit of "+s+" is "+s.charCodeAt(1));

charAt

var s = "length"

for (var i=0;i<s.length;++i) {
    console.log("Char at "+i+" is "+s.charAt(i));
}

Split

• String Separator

var s = "1,2,3"

console.log("The second element is "+s.split(',')[1]);

• Regexp Separator

var s = "my-name_is_foo";
s = s.split(/-|_/).join(" ");
console.log(s);

Substring

var s = "HelloWorld";
s = s.substring(0, "Hello".length+1);
s = s + " Nico";
console.log(s);

toLowerCase

RefDoc

var s = "HelloWorld";
console.log("Hello You !".toLowerCase());

toCapitalize

let capitalizeString = string.charAt(0).toUpperCase() + string.slice(1);

isString

let isString = function(s){
    if (typeof s === 'string' || s instanceof String){
       return true;
    } else {
       return false;
    }
}
let foo = 2;
let bar = "2";
console.log(`foo ${foo} is a string ? `+isString(foo));
console.log(`bar ${bar} is a string ? `+isString(bar));

Delete prefix

• If the prefix is known

let prefix = "pre";
let s = ` ${prefix} text `;
let sWithoutPrefix = s.trim().slice(prefix.length)
console.log(sWithoutPrefix);

Delete suffix

• If the suffix is known

let suffix = "pre";
let s = ` text ${suffix} `;
let sWithoutSuffix = s.trim().slice(0,-suffix.length)
console.log(sWithoutSuffix);

Pad

Pad adds a character to a string until a certain length is reached.

You can pad (add the character):

• at the beginning of the string with padStart ³⁾
• at the end with padEnd

Example with in a date string where you need to have two digits for the month.

let month = 2;
console.log(month.toString().padStart(2,'0'));

integer

To Javascript - Integer

parseInt(string,base)

Example

let i = parseInt("5.01",10);

Validator

https://github.com/validatorjs/validator.js