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javascript (basic of javascript (Objects and the Dom (DOM (document is the…

- - - - <script src = './jsfile.js"> </script>
    - - <script> alert('ddd"); </script>
  - - - Use Camel case
    - - // single line comment in js file
  - - - Developer tool: cmd + option +J
    - - This is for debugging
  - - - let product = ' string';
      - let isbool = true/false
      - variables can start with _ $ letter
      - let total = 122;
      - _accountNumber : private variable
      - $accountName: this is automated variables
      - _ proto _: reserved for non standard features
      - other ways to write variable
        
        let a =0; a=88;
    - - const price = 90;
    - - not recommended, old style
  - - - ++ price vs price++
        
        ++price
        
        increase the variable and then execute
        
        price++
        
        execute first and then increase the variable
    - - cancatenation
        
        message + 2
        
        you can add number to a string and the number will automatically convert to a string
        
        message.toLowerCase();
        
        message.substring(1);
      - message.length;
    - - amount =123
        amount.toString();
      - amount = Number.parseFloat("123.12")
      - if the result is "NaN", it means it is not a number
    - - undefined: let saved;
      - let saved =10; saved = null;
        
        this is to wipe out the value
      - Always use "null", never use "undefined"
    - - Objects: field and methods
        
        let person = {
        firstName: 'John',
        lastName: 'sxx'
        } ;
  - - - === means equal
      - !== means not equal
      - == will convert types, very confusing, try not to use "=="
    - - if(price === 15)
        {
        showMessage("sth");
        }
        else if( price>15)
        {
        action1;
        }
        else{ action3;}
    - - for(let i = 0; i<3; i++) {
        action1;
        }
    - - let count = 1;
        while(count<5){
        console.log(count);
        count++;
        }
      - Do while loop: guarantee the loop will run at least once
        
        do{
        console.log(i);
        i--;
        } while(i>0)
  - - - assign the result of the function to a variable
      - function showMessage{}
        let fn = function () {}
        fn();
      - let myFunc = function showMessage() {}
        myFunc();
  - - - let person = {
        name: 'jone',
        age:32,
        partTime: false};
      - person['age']
      - person.age
    - - let person = {
        name: 'John',
        showInfo: fuction(){
        showMessage(this.name);}
        }
    - - If we pass an object, we are passing the reference of the object
    - - Date
        
        Data.prototype.getDate()
        
        let now = new Date();
        now.toDateString()
      - Math
        
        Math.abs();
        Math.pow();
    - - document is the built in object for web object
      - each element has an ID and it acts as a tag to be referenced to.
      - documentgetElementById('message').textContent = message;
      - we can overide the existing css file with a dom object .style
    - - const button = document.getElementById('see-review');
        button.addEventListener('click', function(){
        console.log('click');
        });
  - - - let values = [ 1, 3, 5];
      - let values = Array.of(1,2,3);
    - - let values = [1,2,3];
        values.slice(1,2);
        
        similar slice methods to python
      - values.splice(1, 0, 'foo') ;
        
        start element, number of the delete element, insert value
    - - values.indexOf('a'); //this returns the index of the element
      - filter()
      - find()
      - forEach()
        values.forEach();
  - - - you can call a fucntion before the function is declared // this is called hoisting