karmen/node_modules/csso/lib/compressor/compress/Dimension.js

var packNumber = require('./Number.js').pack;
var LENGTH_UNIT = {
    // absolute length units
    'px': true,
    'mm': true,
    'cm': true,
    'in': true,
    'pt': true,
    'pc': true,

    // relative length units
    'em': true,
    'ex': true,
    'ch': true,
    'rem': true,

    // viewport-percentage lengths
    'vh': true,
    'vw': true,
    'vmin': true,
    'vmax': true,
    'vm': true
};

module.exports = function compressDimension(node, item) {
    var value = packNumber(node.value);

    node.value = value;

    if (value === '0' && this.declaration) {
        var unit = node.unit.toLowerCase();

        // only length values can be compressed
        if (!LENGTH_UNIT.hasOwnProperty(unit)) {
            return;
        }

        // issue #200: don't remove units in flex property as it could change value meaning
        if (this.declaration.property.name === 'flex') {
            return;
        }

        // issue #222: don't remove units inside calc
        if (this['function'] && this['function'].name === 'calc') {
            return;
        }

        item.data = {
            type: 'Number',
            info: node.info,
            value: value
        };
    }
};