index.js

'use strict';

const FakeTimers = require('jest-util').FakeTimers;
const ModuleMocker = require('jest-mock').ModuleMocker;

function deepCopy(obj) {
    const newObj = {};
    let value;
    for (const key in obj) {
        value = obj[key];
        if (typeof value === 'object' && value !== null) {
            value = deepCopy(value);
        }
        newObj[key] = value;
    }
    return newObj;
}

// Object.assign polyfill with try/catch for each assignment expression
// https://developer.mozilla.org/en/docs/Web/JavaScript/Reference/Global_Objects/Object/assign#Polyfill
function assign(target) {
    if (target === null) {
        throw new TypeError('Cannot convert undefined or null to object');
    }

    const to = Object(target);

    for (let index = 1; index < arguments.length; index++) {
        const nextSource = arguments[index];

        if (nextSource !== null) { // Skip over if undefined or null
            for (const nextKey in nextSource) {
                // Avoid bugs when hasOwnProperty is shadowed
                if (Object.prototype.hasOwnProperty.call(nextSource, nextKey)) {
                    try {
                        to[nextKey] = nextSource[nextKey];
                    }
                    catch (e) {
                        // Any errors are caused by trying to extend node's environment
                    }
                }
            }
        }
    }
    return to;
}

class NodeDebugEnvironment {
    constructor(config) {

        // jest doesn't need full global before runScript, but to reduce possible issues we create full copy here
        this.global = assign({}, global, deepCopy(config.globals));

        this.moduleMocker = new ModuleMocker(global);
        this.fakeTimers = new FakeTimers(this.global, this.moduleMocker, config);
    }

    dispose() {
        if (this.fakeTimers) {
            this.fakeTimers.dispose();
        }
        this.fakeTimers = null;
    }

    runScript(script) {

        // we cannot set global.console to new value (TypeError: Cannot set property console of #<Object> which has only a getter)
        const jestCustomConsole = this.global.console;

        if (jestCustomConsole !== null) {

            // but we can alter properties in any case
            assign(global.console, jestCustomConsole);

            // delete because later we will apply all jest changes from this.global to global
            delete this.global.console;
        }

        assign(global, this.global);

        // it seems Jest hold reference to this.global object and next line doesn't affect, so, we restore console
        this.global.console = jestCustomConsole;

        // during runInThisContext global will be modified (jasmine will set global.jasmineRequire), so, we must set this.global to global (jest will not modify global anymore, so, it is safe)
        this.global = global;

        return script.runInThisContext();
    }
}

module.exports = NodeDebugEnvironment;