List of immutable functions in JavaScript

• 1.0 slice

  // extracts certain section of a string and return a new string
  // doesn't mutate the original string
  
  var name = 'Stephanie Hwang'
  var first = name.slice(0, 8)
  
  console.log(name) //Stephanie Hwang
  console.log(first) //Stepanie
  console.log(name) //Stephanie Hwang

• 2.0 concat

  // concatenate two strings
  // returns a new string
  
  var first = 'Stephanie'
  var last = ' Hwang'
  
  var fullName = first.concat(last);
  
  console.log(first) //Stephanie
  console.log(last) //Hwang
  console.log(fullName) //Stephanie Hwang
  console.log(first) //Stephanie
  console.log(last) //Hwang

• 3.0 replace

  // replaces matching section of a the string which is explicitly passed to replace function
  
  var re = /Harry/gi
  var str = "Harry is a memeber of gryffindor."
  var newstr = str.replace(re, "Hermione")
           
  console.log(str) //Harry is a memeber of gryffindor.
  console.log(newstr) //Hermione is a memeber of gryffindor.
  console.log(str) //Harry is a memeber of gryffindor.

• 4.0 split

  //split a given string into an array of strings
  
  var str = "Apples are round, and apples are juicy.";
  var newstr = str.split(" ", 2);
           
  console.log(str) //Apples are round, and apples are juicy.
  console.log(newstr) //['Apples', 'are']
  console.log(str) //Apples are round, and apples are juicy.

• 5.0 substr

  //extracts part of a string
  
  var str = "Ten points for gryffindor"
  var newstr = str.substr(0, 3)
           
  console.log(str) //Ten points for gryffindor
  console.log(newstr) //Ten
  console.log(str) //Ten points for gryffindor

• 6.0 substring

  //extracts part of a string
  
  var str = "Ten points for gryffindor"
  var newstr = str.substring(0, 3)
           
  console.log(str) //Ten points for gryffindor
  console.log(newstr) //Ten
  console.log(str) //Ten points for gryffindor

• 7.0 toLocaleLowerCase

  //converts string to lowercase by keeping it's current locale
  
  var str = "Ron loves Hermionie"
  var newstr = str.toLocaleLowerCase()
           
  console.log(str) //Ron loves Hermionie
  console.log(newstr) //ron loves hermionie
  console.log(str) //Ron loves Hermionie

• 8.0 toLocaleUpperCase

  //converts string to uppercase by keeping it's current locale
  
  var str = "Ron loves Hermionie"
  var newstr = str.toLocaleUpperCase()
           
  console.log(str) //Ron loves Hermionie
  console.log(newstr) //RON LOVES HERMIONIE
  console.log(str) //Ron loves Hermionie

• 9.0 toString

  //converts type to represent string
  
  var phone = 124587921
  var phonestr = phone.toString()
           
  console.log(phone) //124587921
  console.log(phonestr) // "124587921"
  console.log(phone) //124587921

• 10.0 toLowerCase

  //converts string to lowercase
  
  var str = "Ron loves Hermionie"
  var newstr = str.toLocaleLowerCase()
           
  console.log(str) //Ron loves Hermionie
  console.log(newstr) //ron loves hermionie
  console.log(str) //Ron loves Hermionie

• 11.0 toUpperCase

  //converts string to uppercase
  
  var str = "Ron loves Hermionie"
  var newstr = str.toLocaleUpperCase()
           
  console.log(str) //Ron loves Hermionie
  console.log(newstr) //RON LOVES HERMIONIE
  console.log(str) //Ron loves Hermionie

• 12.0 map

  //iterates through an array
  
  var names = ['rajika', 'stephanie', 'taeyeon']
  names.map(function(name) {
      console.log(name)
  })
  //es6 syntax, arrow function
  //names.map((name) => {
  //  console.log(name)
  //})
  console.log(names)

• 13.0 reduce

  var arr = [1,2,3,4]
  
  var total = arr.reduce(function(prev, curr, index, arr) {
    return prev + curr
  });
  
  console.log(arr) // [1,2,3,4]
  console.log(total) //10
  console.log(arr) // [1,2,3,4]
  //es6 syntax, arrow function
  //var total = arr.reduce((prev, curr, index, arr) => {
    //return prev + curr
  //});