JavaScript
conditions
In JavaScript
we need to ask questions. We always need to run script when a certain condition
is true. And if the condition is true we will execute whatever code is inside
the braces { } .
We will begin
with if statement.
If statement
syntax example:
if
(condition) {
// code goes
here
// …
// …
}
In this
tutorial we will use this terminology - parentheses (), brackets [], and braces
{} . All of these are always found in pairs. If you have an opening one you
will need a closing one. It may be several lines later, but need to be there.
Example for
if statement:
<html>
<head>
<title>Untitled
Document</title>
</head>
<body>
<div
id="demo">
<h1>This
is a heading.</h1>
<p>This
is a paragraph.</p>
</div>
<script>
var a = 20;
var b = 100;
if (a<b) {
console.log("a is
less than b");
}
</script>
</body>
</html>
Always our
condition will be equal to true or false.
We can also
use equality to see if something is equal to something by using these ==.
Example:
<html>
<head>
<title>Untitled
Document</title>
</head>
<body>
<div
id="demo">
<h1>This
is a heading.</h1>
<p>This
is a paragraph.</p>
</div>
<script>
var a = 100;
var b = 100;
if (a == b) {
console.log("a is
equal to b");
}
</script>
</body>
</html>
JavaScript
has another way for checking equality, the triple equal sign. When you want to
ask if something is equal to something you will never use a single equal sign, because
this is assignment not equality and its set a value not checking value. We can
use double if triple equal signs for checking equality: In below
examples we use the if else statement. You will see learn how to use it later
on this chapter.
Example:
<html>
<head>
<title>Untitled
Document</title>
</head>
<body>
<div
id="demo">
<h1>This
is a heading.</h1>
<p>This
is a paragraph.</p>
</div>
<script>
var a =
"100";
var b = 100;
if (a === b)
{
console.log("a is
equal to b");
}
else {
console.log("a is
not strictly equal to b because it's string.");
}
</script>
</body>
</html>
Or if we want
to ask is something is not equal to something, we can do this:
Example:
<html>
<head>
<title>Untitled
Document</title>
</head>
<body>
<div
id="demo">
<h1>This
is a heading.</h1>
<p>This
is a paragraph.</p>
</div>
<script>
var a = 200;
var b = 100;
if (a !== b)
{
console.log("a is
not equal to b");
}
</script>
</body>
</html>
If a is not
equal to be it will alert true, in this case it will alert „a is not
equal to be“.
The curly
braces after the if condition is called blocks. There you add your code, which
will be executed if the condition is true or false. Always use the code blocks.
If you want
to execute some code block if the conditions is equal to false you can follow the
if with the else statement.
Example:
<html>
<head>
<title>Untitled
Document</title>
</head>
<body>
<div
id="demo">
<h1>This
is a heading.</h1>
<p>This
is a paragraph.</p>
</div>
<script>
var a = 200;
var b = 100;
if (a == b) {
console.log("a is equal
to b");
} else {
console.log("a is not
equal to b");
}
</script>
</body>
</html>
OR
<html>
<head>
<title>Untitled
Document</title>
</head>
<body>
<div
id="demo">
<h1>This
is a heading.</h1>
<p>This
is a paragraph.</p>
</div>
<script>
var a = 200;
var b = 100;
if (a == b) {
console.log("a is equal
to b");
}
else {
console.log("a is not
equal to b");
}
</script>
</body>
</html>
Both examples
are similar.
You can also
nest more if’s into the if or else statement, but don’t do that too much deeper
because it will make your code hard to read. Instead of this you can next them
into different function.
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