04 JavaScript Basis 2

1. Function Statements and Expressions

• Function Declariation

• //function declariation
  function whatDoyouDo(job, firstName)
  {
        
        	
  	//...
  }
  
  whatDoyouDo('teacher',John);
  

• function expression

• //function expression
  var whatDoyouDo = function(job, firstName)
  {
        
        
  	//...
  };
  
  whatDoyouDo('teacher',John);
  

  2. Array

• Initialise new array

• var names = ['John', 'Mike', 'Jane'];
  
  var years = new Array(1990,1969,1948);
  

• Length of array

• console.log(years.length);
  

• Mutate array data

• names[1] = 'Ben';
  names[names.length] = 'Mary';
  names[8] = 'Kim';
  

• Different data types

• var john = ['John', 1999, 'happy', false];
  

• Method

• john.push('bule');  //Add a new element to the end
  john.unshift('Mr'); //Add a new element to the beginning
  john.pop(); //Remove the last element
  john.indexOf(1999); //Find the position of the element
  

  3. Objects

• Difference between Array and Objects: Array has order but objects don't.
• Initialise new Object

• //Object literal
  var john = {
        
        
  	firstName: 'John',
  	lastName: 'Smith',
  	birthYear: 1990,
  	family: ['Jame', 'mark', 'Bob', 'Emily'],
  	job: 'teacher',
  	isMarried: false
  };
  

  //new Object syntax
  var jane = new Object();
  jane.name = 'Jane';
  jane.birthYear = 1998;
  jane['lastName'] = 'Smith';
  

• Method

• //Object literal
  var john = {
        
        
  	firstName: 'John',
  	lastName: 'Smith',
  	birthYear: 1990,
  	family: ['Jame', 'mark', 'Bob', 'Emily'],
  	job: 'teacher',
  	isMarried: false,
  	calAge: function()
  	{
        
        
  		this.age =  2019 - this.birthYear;
  	}
  };
  john.calAge();
  console.log(john);
  

  4. Hoisting

• Declaration works with variables and functions

• //works fine VARIABLES
  num+=6;
  var num;
  
  //works fine FUNCTION
  calculateAge(1997);
  function calculateAge(year)
  {
        
        
  	console.log(2019-year);
  }
  

• Expression works fine with variables but does NOT work with functions

• //work fine
  num+=6;
  var num = 0;
  
  //cannot work FUNCTION
  calculateAge(1997);
  var calculateAge = function (year)
  {
        
        
  	console.log(2019-year);
  }
  

  5. Scoping

  var a = 'Hello!';
  first();
  
  function first() {
        
        
      var b = 'Hi!';
      second();
  
      function second() {
        
        
          var c = 'Hey!';
          console.log(a + b + c);
      }
  }
  //input: Hello!Hi!Hey!
  

  var a = 'Hello!';
  first();
  
  function first() {
        
        
      var b = 'Hi!';
      second();
  
      function second() {
        
        
          var c = 'Hey!';
          third();
      }
  }
  
  function third() {
        
        
      var d = 'John';
      console.log(a + b + c + d);
  }
  //input: Uncaught ReferenceError: b is not defined