將從諾言返回的值分配給全局變量

Question

我正在嘗試從量角器讀取瀏覽器內存值，並將其存儲在全局對象中。 為此，我要獲取window.performance.memory對象，然后解決對每個內存值進行檢查的承諾。

問題是我似乎無法將值分配給全局變量。 我已經嘗試了以下代碼，但似乎效果不佳：

 this.measureMemory = function () {

    var HeapSizeLimit;

    browser.driver.executeScript(function () {
        return window.performance.memory;
    }).then(function (memoryValues) {
        HeapSizeLimit = memoryValues.jsHeapSizeLimit;
        console.log('Variable within the promise: ' + HeapSizeLimit);
    });
    console.log('Variable outside the promise: ' + HeapSizeLimit);
};

返回：

   Variable outside the promise: undefined
   Variable within the promise: 750780416

Answer 1

因為console.log('Variable outside the promise: ' + HeapSizeLimit); 在HeapSizeLimit = memoryValues.jsHeapSizeLimit;之前執行 。 如果在約定之后就行了，並不意味着執行順序是相同的。

Answer 2

// a variable to hold a value
var heapSize;

// a promise that will assign a value to the variable
// within the context of the protractor controlFlow
var measureMemory = function() {
    browser.controlFlow().execute(function() {
        browser.driver.executeScript(function() {
            heapSize = window.performance.memory.jsHeapSizeLimit;
        });
    });
};

// a promise that will retrieve the value of the variable
// within the context of the controlFlow
var getStoredHeapSize = function() {
    return browser.controlFlow().execute(function() {
        return heapSize;
    });
};

在您的測試中：

it('should measure the memory and use the value', function() {
    // variable is not yet defined
    expect(heapSize).toBe(undefined);
    // this is deferred
    expect(getStoredHeapSize).toBe(0);

    // assign the variable outside the controlFlow
    heapSize = 0;
    expect(heapSize).toBe(0);
    expect(getStoredHeapSize).toBe(0);

    // assign the variable within the controlFlow
    measureMemory();

    // this executes immediately
    expect(heapSize).toBe(0);
    // this is deferred
    expect(getStoredHeapSize).toBeGreaterThan(0);
};

毫無價值：設置變量和獲取值似乎是同步發生（在controlFlow外部）或異步發生（通過量角器測試中的延遲執行）。