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'use strict';
const { URL } = require('url');
/**
* Get unit from value node
*
* Returns `null` if the unit is not found.
*
* @param {string} urlString
*/
module.exports = function (urlString) {
let protocol = null;
try {
protocol = new URL(urlString).protocol;
} catch {
return null;
}
if (protocol === null || typeof protocol === 'undefined') {
return null;
}
const scheme = protocol.slice(0, -1); // strip trailing `:`
// The URL spec does not require a scheme to be followed by `//`, but checking
// for it allows this rule to differentiate <scheme>:<hostname> urls from
// <hostname>:<port> urls. `data:` scheme urls are an exception to this rule.
const slashIndex = protocol.length;
const expectedSlashes = urlString.slice(slashIndex, slashIndex + 2);
const isSchemeLessUrl = expectedSlashes !== '//' && scheme !== 'data';
if (isSchemeLessUrl) {
return null;
}
return scheme;
};