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javascript [2021/06/05 17:20] – adminjavascript [2021/07/23 14:52] (current) – admin
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 ## Basic ## Basic
 +
 +### Datatype
 +
 +```
 +var length = 16;                               // Number
 +var lastName = "Johnson";                      // String
 +var x = {firstName:"John", lastName:"Doe"};    // Object
 +```
  
 ### Object ### Object
 Create an object with 3 properties: Create an object with 3 properties:
-```+```javascript
 var object = { var object = {
   ID: 1,   ID: 1,
   "name": "Tom",   "name": "Tom",
-  subobject: {+  grade: { 
 +    math: 94 
 +    physics:89
   }   }
-};+  // When a function is used as an object property, it is called a method 
 +  sum: function(a,b){ 
 +    return a+b; 
 +  } 
 +}
 ``` ```
  
-Use dot ```.``` or bracket ```[]``` to access properties +Use dot ```.``` or bracket ```[]``` to access or create properties 
-```+```javascript
 object.ID = object.ID + 1; object.ID = object.ID + 1;
 object["ID"] = object["ID"] + 1; object["ID"] = object["ID"] + 1;
 +object.grade.math = 100;
 +// Method can be called in the same way
 +object.sum(1, 2);
 +
 +// Create new properties or methods in the same way
 object[name + "-full"] = "Tom Hanks"; object[name + "-full"] = "Tom Hanks";
 +object.minus = function(a,b) {
 +  return a-b;
 +};
 ``` ```
  
-Bracket can be used to create new properties+### Question Mark "?"
  
 +Three use of question mark: [[https://www.freecodecamp.org/news/how-the-question-mark-works-in-javascript/|Link]]
  
 ## jQuery ## jQuery
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 A jQuery action() to be performed on the element(s)\\ A jQuery action() to be performed on the element(s)\\
  
- +By default, jQuery uses "\$" as a shortcut for "jQuery". Doing ````var $=function(){}```` is just defining a function called "\$", it is very same as doing ````var a=function(){}````
-### The $ mark +
-By default, jQuery uses "$" as a shortcut for "jQuery".  +
- +
-Doing ````var $=function(){}```` is just defining a function called "\$", it is very same as doing ````var a=function(){}````+
  
  
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 ``` ```
  
-The pseudo-code for that block is: +The pseudo-code for that block is: When the document object model ````$(document) is ready .ready()````, call the following function ````function() {  }````. In that function, check for all ````<li>````'s on the page ````$('li')```` and using the jQuery method .CSS() to set the CSS property "color" to the value "red" ````.css('color', 'red')````;
- +
-When the document object model ````$(document) is ready .ready()````, call the following function ````function() {  }````. In that function, check for all ````<li>````'s on the page ````$('li')```` and using the jQuery method .CSS() to set the CSS property "color" to the value "red" ````.css('color', 'red')````;+
  
  
 ### Functions in jQuery ### Functions in jQuery
  
-**Example:** hide the current element+Example: hide the current element
 ```javascript ```javascript
 $(this).hide()  $(this).hide() 
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 ``` ```
  
-#### Create your own functions (plugins)+#### jQuery plugins
 Example: to create a plugin that makes text within a set of retrieved elements green. All we have to do is add a function called greenify to ```$.fn``` and it will be available just like any other jQuery object method. Example: to create a plugin that makes text within a set of retrieved elements green. All we have to do is add a function called greenify to ```$.fn``` and it will be available just like any other jQuery object method.
  
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 JavaScript statements are executed line by line. However, with effects, the next line of code can be run even though the effect is not finished. This can create errors. JavaScript statements are executed line by line. However, with effects, the next line of code can be run even though the effect is not finished. This can create errors.
  
-To prevent this, you can create a callback function. +To prevent this, you can create a callback function. A callback function is executed after the current effect is finished. Typical syntax: ```$(selector).hide(speed,callback);```
- +
-A callback function is executed after the current effect is finished. +
- +
-Typical syntax: ```$(selector).hide(speed,callback);```+
  
 Example: Example:
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 ```javascript ```javascript
 $("#p1").css("color", "red").slideUp(2000).slideDown(2000); $("#p1").css("color", "red").slideUp(2000).slideDown(2000);
 +```
 +
 +#### Normal javascript function in jQuery?
 +You might want to just have a function in jQuery to use the query features. However it could not be called outside of the jQuery namespace. Here's an example:
 +```javascript
 +$(document).ready( function () {
 +    var MyBlah = function(blah) { alert(blah);  };
 +    MyBlah("Hello this works") // Inside the anonymous function we are cool.
 + });
 +
 +MyBlah("Oops") //This throws a JavaScript error (MyBlah is not a function)
 +```
 +
 +This is (sometimes) a desirable behavior since we do not pollute the global namespace, so if your function does not need to be called from other part of your code, this is the way to go.
 +
 +Declaring it outside the anonymous function places it in the global namespace, and it's accessible from everywhere.
 +
 +If you want to call it anywhere, use the `$.` namespace:
 +```javascript
 +$(document).ready( function () {
 +    $.MyBlah = function(blah) { alert(blah);  };
 +    MyBlah("Hello this works") // Inside the anonymous function we are cool.
 + });
 +
 +$.MyBlah("Oops") //This throws a JavaScript error (MyBlah is not a function)
 ``` ```
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