echo "foo bar" | node sed 's/foo/[$0]/g'

sed.js

const replacementExpression = /^s\/((?:\\.|[^\/\\])+)\/((?:\\.|[^\/\\])*)\/([gimuy]{0,5})$/
const replacementExpressionCompiled = replacementExpression.exec(process.argv[2])

function getReplacement (input, source, flags, replacement) {
	const expression = new RegExp(source, flags)

	return input.replace(expression, function (matched/*, ...captures, index, fulltext, groups? */) {
		const parameters = Array.from(arguments)

		const [index, fulltext, groups] =
			typeof arguments[arguments.length - 1] === 'object' ?
			parameters.splice(-3) :
			parameters.splice(-2)

		const captures = parameters.splice(1)

		return replacement
			.replace(/(?:\\|\$)(\d+)/g, (x, y) => ([matched, ...captures])[Number.parseInt(y)] || x)
	})

}

process.stdin.on('data', buffer => {
	process.stdout.write(
		getReplacement(buffer.toString(),
		replacementExpressionCompiled[1],
		replacementExpressionCompiled[3],
		replacementExpressionCompiled[2]))
})

this will probably do the same thing

const replacementExpression = /^s\/((?:\\.|[^\/\\])+)\/((?:\\.|[^\/\\])*)\/([gimuy]{0,5})$/
const replacementExpressionCompiled = replacementExpression.exec(process.argv[2])

process.stdin.on('data', buffer => {
	process.stdout.write(
	buffer.toString().replace(
		new RegExp(replacementExpressionCompiled[1], replacementExpressionCompiled[3]),
		replacementExpressionCompiled[2] ))
})