butternut/src/program/types/TemplateLiteral.js

Experimental ES2015-aware minifier

import Node from '../Node.js';
import { UNKNOWN } from '../../utils/sentinels.js';
import stringify from '../../utils/stringify.js';

export default class TemplateLiteral extends Node {
	getValue () {
		let values = new Array( this.expressions.length );
		let i;

		for ( i = 0; i < this.expressions.length; i += 1 ) {
			const expression = this.expressions[i];
			const value = expression.getValue();

			if ( value === UNKNOWN ) return UNKNOWN;

			values[i] = value;
		}

		let result = '';

		for ( i = 0; i < this.expressions.length; i += 1 ) {
			const value = values[i];

			result += this.quasis[i].value.raw;
			result += value;
		}

		result += this.quasis[i].value.raw;

		return result;
	}

	minify ( code, chars ) {
		if ( this.parent.type !== 'TaggedTemplateExpression' ) {
			const value = this.getValue();

			if ( value !== UNKNOWN ) {
				code.overwrite( this.start, this.end, stringify( value ) );
				return;
			}
		}

		let c = this.start;
		let i;
		for ( i = 0; i < this.expressions.length; i += 1 ) {
			const quasi = this.quasis[i];
			const nextQuasi = this.quasis[i+1];
			const expression = this.expressions[i];

			const value = expression.getValue();
			if ( typeof value === 'object' ) { // includes both UNKNOWN and known non-primitives
				expression.minify( code, chars );

				if ( expression.start > quasi.end + 2 ) {
					code.remove( quasi.end + 2, expression.start );
				}

				c = ( nextQuasi ? nextQuasi.start : this.end ) - 1;
				if ( expression.end < c ) code.remove( expression.end, c );
			} else {
				code.overwrite( quasi.end, expression.end, String( value ) );
				c = ( nextQuasi ? nextQuasi.start : this.end - 1 );
				if ( expression.end < c ) code.remove( expression.end, c );
			}
		}

		const lastQuasi = this.quasis[i];

		if ( lastQuasi.start > c + 1 ) {
			code.remove( c, lastQuasi.start - 1 );
		}
	}
}