Tip: use JavaScript as a calculator in Firefox and Chrome

Axel Rauschmayer

Jun. 10, 11 · Web Dev Zone · Interview

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The following tip allows you to quickly perform calculations via JavaScript in Firefox and Chrome.

Basic idea: If you enter a javascript: URL in Firefox, the result of the expression is shown in the window. For example, try the following URL:

javascript:7*45

Firefox: By using a keyword [1], you can save 8 keystrokes (9 if your keyword is j instead of js). Just create the following bookmark:

Now you can perform the above calculation by typing

    js 7*45

Google Chrome: handles output and keywords differently than Firefox.

JavaScript code to display a result: As Webkit browsers don’t replace the page content with the result of a JavaScript expression, you need to explicitly display the result, e.g. via alert():
```
    javascript:alert(7*45)
```
Creating a keyword: Go to “Preferences → Basics → Search → Manage Search Engines...” and create a new entry with the following URL:
```
    javascript:alert(%s)
```

JavaScript you can use:

Arithmetic operators: addition (+), subtraction (-), multiplication (*), and division (/), modulo (%).
```
    > 77 / 11
    7
    > 3.16 * 5
    15.8
    > 10 % 7
    3
```
Properties and methods of the global Math object [2]:
- Math.PI
- Math.pow(base, exponent)
- Math.sqrt(x)
- Math.sin(x)
Converting to and from hexadecimal, binary, etc.
```
    > (255).toString(16)
    'ff'
    > parseInt("ff", 16)
    255
```
You need to put the number in parenthesis to invoke a method on it. Otherwise the dot will be mistaken as a decimal point. Alternatively, you can type two dots or append .0 to the number.

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