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=== If-Statements ===
If statements are used to tell the browser ''"if this condition is currently true, do this"''. An if statement is structured like this:

<syntaxhighlight lang="javascript">
if (the condition) {
    code to run
}
</syntaxhighlight>

For example you could make the loaded document (in the browser) prompt for the user to type in their age, and if it is below 21, it would then proceed to the instruction to write an output: "No beer for you!".

The code to embed would be this:

<syntaxhighlight lang="javascript">
<script>
var age = prompt("How old are you?","");
if (age < 21) {
    document.write("No beer for you!");
};
</script>
</syntaxhighlight>