index.js

'use strict';

var postcss = require('postcss');
var objectAssign = require('object-assign');

var defaults = {
    unitToConvert: 'px',
    viewportWidth: 320,
    viewportHeight: 568, // not now used; TODO: need for different units and math for different properties
    unitPrecision: 5,
    viewportUnit: 'vw',
    fontViewportUnit: 'vw',  // vmin is more suitable.
    filePathBlackList: [],
    minPixelValue: 1,
    mediaQuery: false
};

module.exports = postcss.plugin('postcss-px-to-viewport', function (options) {

    var opts = objectAssign({}, defaults, options);
    var pxReplace = createPxReplace(opts.viewportWidth, opts.minPixelValue, opts.unitPrecision, opts.viewportUnit);

    // excluding regex trick: http://www.rexegg.com/regex-best-trick.html
    // Not anything inside double quotes
    // Not anything inside single quotes
    // Not anything inside url()
    // Any digit followed by px
    // !singlequotes|!doublequotes|!url()|pixelunit
    var pxRegex = new RegExp('"[^"]+"|\'[^\']+\'|url\\([^\\)]+\\)|(\\d*\\.?\\d+)' + opts.unitToConvert, 'ig')

    return function (css) {

        css.walkDecls(function (decl, i) {
            // This should be the fastest test and will remove most declarations

            if (decl.value.indexOf(opts.unitToConvert) === -1) return;

            if (blacklistedFilePathSelector(opts.filePathBlackList, decl.parent.source.input.file)) {
                return;
            }


            var unit = getUnit(decl.prop, opts)

            decl.value = decl.value.replace(pxRegex, createPxReplace(opts.viewportWidth, opts.minPixelValue, opts.unitPrecision, unit));
        });

        if (opts.mediaQuery) {
            css.walkAtRules('media', function (rule) {
                if (rule.params.indexOf(opts.unitToConvert) === -1) return;
                rule.params = rule.params.replace(pxRegex, pxReplace);
            });
        }

    };
});

function getUnit(prop, opts) {
    return prop.indexOf('font') === -1 ? opts.viewportUnit : opts.fontViewportUnit;
}

function createPxReplace(viewportSize, minPixelValue, unitPrecision, viewportUnit) {
    return function (m, $1) {
        if (!$1) return m;
        var pixels = parseFloat($1);
        if (pixels <= minPixelValue) return m;
        return toFixed((pixels / viewportSize * 100), unitPrecision) + viewportUnit;
    };
}

function toFixed(number, precision) {
    var multiplier = Math.pow(10, precision + 1),
        wholeNumber = Math.floor(number * multiplier);
    return Math.round(wholeNumber / 10) * 10 / multiplier;
}

function blacklistedFilePathSelector(blacklist, fileName) {
    return blacklist.some(function (regex) {
        return fileName.indexOf(regex) > 0;
    });
}