Color Contast Checker

An accessibility checker tool for validating the color contrast based on WCAG 2.0 and WCAG 2.1 standard.

The formula (L1/L2) for contrast is based on [ISO-9241-3] and [ANSI-HFES-100-1988] standards as described here :

http://www.w3.org/TR/2008/REC-WCAG20-20081211/#relativeluminancedef
http://www.w3.org/TR/WCAG20/#contrast-ratiodef
https://www.w3.org/TR/WCAG21/#contrast-minimum

It also supports shorthand color codes e.g #FFF or #000 etc.

https://www.w3.org/TR/2001/WD-css3-color-20010305#colorunits

Installation:
------------

``
npm install color-contrast-checker
`
or using package.json

`
{
"name": "my-app",
..
"devDependencies": {
..
"color-contrast-checker": "2.1.0"
}
}
`
Then do npm install

Usage:
-----

To check specific WCAG levels
`
var ccc = new ColorContrastChecker();

var color1 = "#FFFFFF";
var color2 = "#000000;

if (ccc.isLevelAA(color1, color2, 14)) {
alert("Valid Level AA");
} else {
alert("Invalid Contrast");
}

`

To check custom ratios
`
var ccc = new ColorContrastChecker();

var color1 = "#FFFFFF";
var color2 = "#000000;
var customRatio = 5.7;

// No need for font size, now that we are using a custom ratio.
// This is because we are no longer checking against WCAG requirements.
if (ccc.isLevelCustom(color1, color2, customRatio)) {
alert("Above given ratio");
} else {
alert("Invalid Contrast");
}

`

Advanced Usage:
--------------

You can pass pairs and get results:


`
var pairs = [
{
'colorA': '#000000',
'colorB': '#000000', // All should fail
'fontSize': 14
},
{
'colorA': '#000000',
'colorB': '#FFFFFF', //All should pass
'fontSize': 14
},
{
'colorA': '#000000',
'colorB': '#848484', //AAA should fail
'fontSize': 14
},
{
'colorA': '#000000',
'colorB': '#848484', //All should pass (because of font)
'fontSize': 19
},
{
'colorA': '#000000',
'colorB': '#757575', //AA should pass AAA should fail
'fontSize': 14
},
{
'colorA': '#000000',
'colorB': '#656565', //All should fail
'fontSize': 14
}
];

var results = ccc.checkPairs(pairs);

`

The result will look like this:

`
[
{
'WCAG_AA' : false,
'WCAG_AAA': false
},
{
'WCAG_AA' : true,
'WCAG_AAA': true
},
{
'WCAG_AA' : true,
'WCAG_AAA': false
},
{
'WCAG_AA' : true,
'WCAG_AAA': true
},
{
'WCAG_AA' : true,
'WCAG_AAA': false
},
{
'WCAG_AA' : false,
'WCAG_AAA': false
}
]
`

Tests

npm test`

Contributing

In lieu of a formal style guide, take care to maintain the existing coding style. Add unit tests for any new or changed functionality. Lint and test your code.