feature-detect.js.ejs

var unsupportedFeatures = []

function test(script, name) {
	try {
		eval(script)
	} catch (err) {
		unsupportedFeatures.push(name)
		console.error(err)
	}
}

test("let val = 'a'", 'let')
test("const arr = 'a'", 'const')
test('var str = `abc`', 'backticks')
test("'a'.includes('b')", 'String.prototype.includes')
test("['a'].includes('b')", 'Array.prototype.includes')
test("['a'].map(elem => elem + 'b')", 'arrow functions')
test("document.createElement('div').remove()", 'ChildNode.remove')
test('var a = document.currentScript.src', 'document.currentScript')

if (unsupportedFeatures.length > 0) {
	var errorMessage =
		'Browser does not support some features required by <%= projectName %> (' +
		unsupportedFeatures.join(', ') +
		'), please either use a more modern browser (ideally Chrome) or report a bug at <%= bugReportUrl %>.'
	try {
		console.log(errorMessage)
		<% if (!!writeFeatureErrorsToDom) { %>
			document.write(errorMessage)
		<% } else { %>
			alert(errorMessage)
		<% } %>
		document.execCommand('Stop')
	} catch (err) {
		console.error(err)
		//catch but just log so we can continue to try to throw the more helpful error message
	}
	throw Error(errorMessage)
}