webpack/lib/UseStrictPlugin.js

/*
	MIT License http://www.opensource.org/licenses/mit-license.php
	Author Tobias Koppers @sokra
*/
"use strict"

const ConstDependency = require("./dependencies/ConstDependency");

class UseStrictPlugin {
	apply(compiler) {
		compiler.plugin("compilation", (compilation, params) => {
			params.normalModuleFactory.plugin("parser", (parser) => {
				let parserInstance = parser;
				parser.plugin("program", (ast) => {
					let firstNode = ast.body[0];
					let dep;
					if(firstNode &&
						firstNode.type === "ExpressionStatement" &&
						firstNode.expression.type === "Literal" &&
						firstNode.expression.value === "use strict") {
						// Remove "use strict" expression. It will be added later by the renderer again.
						// This is necessary in order to not break the strict mode when webpack prepends code.
						// @see https://github.com/webpack/webpack/issues/1970
						dep = new ConstDependency("", firstNode.range);
						dep.loc = firstNode.loc;
						parserInstance.state.current.addDependency(dep);
						parserInstance.state.module.strict = true;
					}
				});
			})
		})
	}
}

module.exports = UseStrictPlugin;