Color Contrast 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

const ccc = new ColorContrastChecker();

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

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

To check custom ratios

const ccc = new ColorContrastChecker();

const color1 = "#FFFFFF";
const color2 = "#000000";
const 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:

    const 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.