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Re: Javascript Tutorial From The Scratch Brought to you from Part 1 by Nobody: 9:07pm On Jul 03, 2014 |
Chapter 08. If Statements: Check user responses with if statements One of the most important features of a computer language is the capability to test and compare values. This allows your scripts to behave differently based on the values of variables, or based on input from the user. The if statement is the main conditional statement in JavaScript. This statement means much the same in JavaScript as it does in English—for example, here is a typical conditional statement in English: If the phone rings, answer it. This statement consists of two parts: a condition (If the phone rings) and an action (answer it). The if statement in JavaScript works much the same way. Here is an example of a basic if statement: Example 1: this will not yield any result since the condition is not yet meth if (a == 1) window.alert('Found a 1!'); This statement includes a condition (if a equals 1) and an action (display a message). This statement checks the variable a and, if it has a value of 1, displays an alert message. Otherwise, it does nothing. If you use an if statement like the preceding example, you can use a single statement as the action. You can also use multiple statements for the action by enclosing them in braces ({}), as shown here: Example 2: this will yield result because the condition was met initially. var a=1; This block of statements checks the variable a once again. If it finds a value of 1, it displays a message and sets a back to 0. Conditional Operators While the action part of an if statement can include any of the JavaScript statements you've already learned (and any others, for that matter), the condition part of the statement uses its own syntax. This is called a conditional expression. A conditional expression includes two values to be compared (in the preceding example, the values were a and 1). These values can be variables, constants, or even expressions in themselves. Note: Either side of the conditional expression can be a variable, a constant, or an expression. You can compare a variable and a value, or compare two variables. (You can compare two constants, but there's usually no reason to.) Between the two values to be compared is a conditional operator. This operator tells JavaScript how to compare the two values. For instance, the == operator is used to test whether the two values are equal. A variety of conditional operators are available: Using Comparison Operators / Conditional Operators In Javascript == (is equal to) != (is not equal to) === (equal value and equal type) !== (not equal value or not equal type) < (is less than) > (is greater than) >= (is greater than or equal to) <= (is less than or equal to) Example 3a: Note that x is an integer here var x = 5; Example 3b: Note that x is a string here var x = '5'; Both will give the same result, however, using === which compares both values and variable types, a different result will be seen Example 4a: Note that x is an integer here var x = 5; Example 4b: Note that x is a string here var x = '5'; Example 5: using comparison var x=5,y=8; Note: Be sure not to confuse the equality operator (==) with the assignment operator (=), even though they both might be read as "equals." Remember to use = when assigning a value to a variable, and == when comparing values. Confusing these two is one of the most common mistakes in JavaScript programming. |
Re: Javascript Tutorial From The Scratch Brought to you from Part 1 by Nobody: 9:08pm On Jul 03, 2014 |
Chapter 09. Boolean values: true & false Boolean logic is something used in most programming languages, including JavaScript. It's very useful to know at least a little bit about it. In JavaScript, you mostly need it in if() statements. In Boolean logic, a statement can have two values, true or false. When using Boolean logic in philosophy, the statement can be a sentence, like It rains today.In more down-to-earth applications like JavaScript, a statement is something like x == 4Both statements can be either true or false. When writing a program it is often necessary to see if a statement is true or false. Usually this is done by an if() statement. If the statement x == 4 is true, then do something:
All this is not surprising. Boolean logic, however, also offers possibilities to evaluate a whole string of statements and see whether the whole string is true or false. Like: It rains today AND my feet are getting wetIn Boolean logic, this longer statement is true if it rains today is true AND my feet are getting wet is true. It rains today OR my feet are getting wetIn Boolean logic, this statement is true if it rains today is true OR if your feet are getting wet is true OR if both statements are true. This is also very useful when writing programs. For instance, suppose you want to do something if x==4 OR y==1. Then you write: if (x==4 || y==1) {The statement (x==4 || y==1) is true when x is 4 OR y is 1. Source: http://www.quirksmode.org/js/boolean.html |
Re: Javascript Tutorial From The Scratch Brought to you from Part 1 by Nobody: 6:00am On Jul 04, 2014 |
Chapter 10. Confirm Box: The confirm command This is used to confirm a user about certain action, and decide between two choices depending on what the user chooses. Syntax: window.confirm() Note that the value x is a boolean value, the value will be TRUE if okay is clicked, and FALSE when cancel is clicked. Example: var x=window.confirm('Are you sure you are ok?'); It can also be rewritten like this: var x=window.confirm('Are you sure you are ok?'); or var x=window.confirm('Are you sure you are ok?'); |
Re: Javascript Tutorial From The Scratch Brought to you from Part 1 by Nobody: 6:14am On Jul 04, 2014 |
Chapter 11. Null value: The special value null Most programming languages have only one value for “no value” or “empty reference”. For example, that value is null in Java. JavaScript has two of those special values: undefined and null. They are basically the same (something that will change with ECMAScript 6, as will be explained in the last post of this series), but they are used slightly differently. undefined is assigned via the language itself. Variables that have not been initialized yet have this value: null is used by programmers to explicitly indicate that a value is missing. Example 1: In this example, v was declared as a variable, but it was never assigned a value, so the value is undefined. var v; Example 2a: How to differentiate between undefined and null.
Example 2b: How to differentiate between undefined and null.
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Re: Javascript Tutorial From The Scratch Brought to you from Part 1 by Nobody: 6:26am On Jul 04, 2014 |
Chapter 12. If Conditions: Combining conditions with && and || We have looked at the comparison operators above (>,<,==,=== etc), now, we want to learn how to write more extended if statements using logical operators. The Logical Operators are: && (and) || (or) ! (not) Example 1: if either condition is true, the entire statement returns true if ((20 > 500) || (50 < 200)) { Example 2: if both conditions are true, then the entire statement returns true if ((20 > 500) && (50 < 200)) { Example 3: using not. Not causes reversal of conditions, i.e changes true to false and false to true. if ((20 != 500) && (50 != 200)) { Example 4: this will not give any result if ((20 != 20) && (50 != 200)) { Javascript Conditional Operator JavaScript also contains a conditional operator that assigns a value to a variable based on some condition. Syntax: variablename = (condition) ? value1:value2 Consider this statement: var age=15; it can be rewritten using the conditional operator as shown below with exactly the same result: var age=15; |
Re: Javascript Tutorial From The Scratch Brought to you from Part 1 by Godmother(f): 6:29am On Jul 04, 2014 |
Hmmmm! Programming is not beans! I decided to wait till this early to read this tutorial and my brain still feels fried. Will start frm d beginning again cos I MUST learn this tin. Kudos dhtml for this. This is really appreciated. 1 Like |
Re: Javascript Tutorial From The Scratch Brought to you from Part 1 by Nobody: 7:09am On Jul 04, 2014 |
13. While loop: Repeat code with while loops Loops can execute a block of code as long as a specified condition is true. The while loop loops through a block of code as long as a specified condition is true. Syntax: while (condition) { Example: this will iterate the value of i from 1 to 5. var i=1; There are more complicated ways of using while, but this will suffice for now. |
Re: Javascript Tutorial From The Scratch Brought to you from Part 1 by Nobody: 7:13am On Jul 04, 2014 |
And so we come to the end of tutorial, i intentionally removed processing ajax requests because it will complicate things. This tutorial is for beginners and does not expect you to know more than HTML. |
Re: Javascript Tutorial From The Scratch Brought to you from Part 1 by Nobody: 9:16am On Jul 04, 2014 |
zz |
Re: Javascript Tutorial From The Scratch Brought to you from Part 1 by Nobody: 9:29am On Jul 04, 2014 |
*dhtml: What about the robot challenge. |
Re: Javascript Tutorial From The Scratch Brought to you from Part 1 by Nobody: 2:20pm On Jul 04, 2014 |
I am leaving every other thing for the next class. I want this section to be as simple as possible. |
Re: Javascript Tutorial From The Scratch Brought to you from Part 1 by Nobody: 1:32pm On Jul 05, 2014 |
Please *dhtml, how do you assign a variable dynamically in javascript let's say if you want to take a value from a form input and display it with document.write(do something); or alert(do something); Or probably use it with a condition statement. |
Re: Javascript Tutorial From The Scratch Brought to you from Part 1 by Nobody: 1:45pm On Jul 05, 2014 |
You need to illustrate what you wish to do clearly. Are you speaking of form validation? Because that is when you can speak of retrieving the form fields as variables and checking whether they are empty and decide on what to do. |
Re: Javascript Tutorial From The Scratch Brought to you from Part 1 by Nobody: 1:58pm On Jul 05, 2014 |
Ok this is what I am trying to achieve <form id="myForm">
But the script above is not working. |
Re: Javascript Tutorial From The Scratch Brought to you from Part 1 by Nobody: 2:43pm On Jul 05, 2014 |
It should be: var x = document.getElementById('myForm').dhtml.value;But document.write will not work unless the page is still loading, you can use alert instead, let me provide a full html example - although your question is beyond the scope of this class. example.html <html> |
Re: Javascript Tutorial From The Scratch Brought to you from Part 1 by Nobody: 7:01pm On Jul 05, 2014 |
Well, I was strictly adhering to my father's advice to always read ahead of my teachers. Thanks and when will you start part 2 @ *dhtml |
Re: Javascript Tutorial From The Scratch Brought to you from Part 1 by dhtml(m): 8:40pm On Jul 07, 2014 |
I heard some students could not even find this thread. |
Re: Javascript Tutorial From The Scratch Brought to you from Part 1 by adewasco2k(m): 9:43pm On Jul 07, 2014 |
dhtml: I heard some students could not even find this thread. and such thread doesnt make FP. no worries, im learning and following |
Re: Javascript Tutorial From The Scratch Brought to you from Part 1 by Smooth51(m): 10:13pm On Jul 07, 2014 |
oga dhtml i have been looking for ways to learn js...doing it myself isn't working as i get bored.........i am joining your class by tommorow my bug note will be ready |
Re: Javascript Tutorial From The Scratch Brought to you from Part 1 by dhtml(m): 10:47am On Jul 12, 2014 |
adewasco2k:If it gets to frontpage, a lot of trolls will come in and scatter the thread with nonsense talks. Thank you all for attending this class, we are now advancing forward. My stock exchange API that is supposed to reach frontpage no hit am, it is the man that pregnant his sister that is hitting frontpage. We shall soon go into the part 2 of the tutorial, but first, let us visit the workshop of this class and continue from there. Creating A Simple Calculator With Raw Javascript |
Re: Javascript Tutorial From The Scratch Brought to you from Part 1 by Nobody: 11:16am On Jul 12, 2014 |
dhtml: |
Re: Javascript Tutorial From The Scratch Brought to you from Part 1 by dhtml(m): 11:53pm On Jul 12, 2014 |
The part 2 of the tutorial is kicking off here, leave that calculator alone if it is bugging you now. https://www.nairaland.com/1810544/javascript-tutorial-scratch-brought-#24648523 |
Re: Javascript Tutorial From The Scratch Brought to you from Part 1 by Nobody: 8:34am On Aug 10, 2014 |
Sorry for the break in transmission people, I have copied the complete tutorial here and also included the eBook which contains part 1 and a little bit of part 2. I am writing a new JavaScript Book titled "Event Driven Programming With JavaScript". |
Re: Javascript Tutorial From The Scratch Brought to you from Part 1 by Nastydroid(m): 12:21am On Aug 11, 2014 |
It is good this way bro |
Re: Javascript Tutorial From The Scratch Brought to you from Part 1 by Nobody: 7:18am On Aug 11, 2014 |
Thanks bro, the part 2 will come out this week. |
Re: Javascript Tutorial From The Scratch Brought to you from Part 1 by Nobody: 3:05am On Aug 25, 2014 |
Sorry guys that I have not released the part 2 tutorial yet as promised, it was due to some upgrades I did on my blog. All developers and programmers can benefit from it, please check www.dhtmlhub.com - I shall make the tutorial available really and shall publish it on this thread when i am done. |
Re: Javascript Tutorial From The Scratch Brought to you from Part 1 by Nmeri17: 12:05am On Feb 25, 2015 |
just curious but does anyone know what lies outside the global variable?? |
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