JavaScript Reference

Quick Reference

The if…else statement executes a block of code if a specified condition is true, and optionally, another block of code if false.

In an if…else statement, we can have the following:

  • if – a block of code to be executed if a condition is true
  • else if (optional) – a new condition to test, and new block of code to be executed, if the first condition is false, but the new condition is true
  • else (optional) – a block of code to be executed if the none of the conditions are true
<!-- html element to place output -->
<p id="my_output"></p>

The following checks what the hour of the day is and then looks at the “if” to see if that is true. If not, it looks at the “else if” to see if that is true. If neither is true, it will use the code within the “else”.

// variables
let my_hour = new Date().getHours();
let my_greeting = '';

// conditions
if (my_hour < 12) {
    my_greeting = 'Good morning';
}
else if (my_hour < 18) {
    my_greeting = 'Good afternoon';
}
else {
    my_greeting = 'Good evening';
}

// output to HTML element
document.getElementById('my_output').innerHTML = my_greeting;

Output

Good afternoon

Syntax

if (condition) {
    // code to run if true
}
if (condition) {
    // code to run if true
}
else {
    // code to run if the condition above is false
}
if (condition) {
    // code to run if true
}
else if (new condition) {
    // code to run if true
}
else {
    // code to run if both conditions above are false
}

Note

Although you are required to have the “if” statement, you don’t have to have the “else if” or “else” statements following. Also, although you can only have one “if” statement and one “else” statement, you could have multiple “else if” statements in between. However, that may be a situation where the switch statement is a better fit.


JavaScript Notes:

  • When using JavaScript, single or double quotation marks are acceptable and work identically to one another; choose whichever you prefer, and stay consistent
  • JavaScript is a case-sensitive language; firstName is NOT the same as firstname
  • Arrays count starting from zero NOT one; so item 1 is position [0], item 2 is position [1], and item 3 is position [2] … and so on
  • JavaScript variables must begin with a letter, $, or _
  • JavaScript variables are case sensitive (x is not the same as X)

We’d like to acknowledge that we learned a great deal of our coding from W3Schools and TutorialsPoint, borrowing heavily from their teaching process and excellent code examples. We highly recommend both sites to deepen your experience, and further your coding journey. We’re just hitting the basics here at 1SMARTchicken.