10 Angular interview questions that range from happy to sad

Although there are only 10 questions, they cover all aspects of angular development, including basic knowledge points, problems encountered during the development process, and more open questions. To identify the interviewer's basic level and project experience, if you were interviewing a year ago, it would definitely be a transition from comedy to tragedy? (PS: The answer is for reference only~).

Related tutorial recommendations: "angular Tutorial"

1. ng-show/ng-hide and ng-if## The difference between #?

We all know that ng-show/ng-hide actually hides and displays through

display. And ng-if actually controls the addition and deletion of dom nodes. Therefore, if we load DOM nodes based on different conditions, then the performance of ng-if is better than ng-show.

2. Explain what

$rootScrope and and# The difference between ##$scope? In layman terms

$rootScrope

is the father of all $scope on the page.

Let’s take a look at how to generate

$rootScope

and $scope. step1: Angular parses

ng-app

and creates $rootScope in memory. step2: Angular returns to continue parsing, finds the

{{}}

expression, and parses it into a variable. step3: Then the div with

ng-controller

will be parsed and pointed to a controller function. At this time, the controller function becomes a $scope object instance. 3. How does the expression

{{yourModel}}

work? It relies on the $interpolation service. After initializing the page html, it will find these expressions and mark them, so every time it encounters a

{{}}

, it will set a $watch. And $interpolation will return a function with context parameters. When the function is finally executed, the expression $parse is transferred to that scope. 4. What is the digest cycle in Angular?

In each digest cycle, angular will always compare the value of the model on the scope. Generally, the digest cycle is automatically triggered. We can also use $apply to trigger manually. For deeper research, you can move to

The Digest Loop and apply

. 5. How to cancel

$timeout

, and stop a $watch()?To stop $timeout we can use cancel:

var customTimeout = $timeout(function () {
  // your code
}, 1000);

$timeout.cancel(customTimeout);

Stop a

$watch

:<pre class='brush:php;toolbar:false;'>// .$watch() 会返回一个停止注册的函数 function that we store to a variable var deregisterWatchFn = $rootScope.$watch(‘someGloballyAvailableProperty’, function (newVal) { if (newVal) { // we invoke that deregistration function, to disable the watch deregisterWatchFn(); ... } });</pre>6. How can I set the restrict in Angular Directive? What is the difference between @,=,& in scope?

restrict can be set separately:

• A

  Matching attributes

• E

  Match tag

• C

  Match class

##M
• Match comment
  Of course you can set multiple values ​​such as
AEC

to perform multiple matches.

In the scope, @,=,& represent respectively when doing value binding

@
• Get a set string, it You can set it yourself or use {{yourModel}} for binding;

=
• Two-way binding, binding some properties on the scope;

&
• is used to execute some expressions on the parent scope. Commonly we set some functions that need to be executed

  angular.module('docsIsolationExample', [])
  .controller('Controller', ['$scope', function($scope) {
    $scope.alertName = function() {
        alert('directive scope &');
    }
  }])
  .directive('myCustomer', function() {
    return {
      restrict: 'E',
      scope: {
        clickHandle: '&'
      },
      template: &#39;<button ng-click="testClick()">Click Me</button>&#39;,
      controller: function($scope) {
        
        $scope.testClick = function() {
          $scope.clickHandle();
          
        }  
      }
    };
  });

  <div ng-app="docsIsolationExample">
  <div ng-controller="Controller">
    <my-customer click-handle="alertName()"></my-customer>
  </div>
   </div>

Codepen Demo: https://codepen.io/Jack_Pu/pen/NrpRBK

Perform one-way binding.
7. List at least three ways to implement communication between different modules?

Service

• events, specify the bound event

• Use $rootScope

• Directly use
$parent
• ,

  $$childHead, etc.

  directive to specify attributes between
• ##directive data. Binding

8. What measures can be taken to improve Angular performance

• Officially recommended, turn off debug,

  $compileProvider

myApp.config(function ($compileProvider) {
  $compileProvider.debugInfoEnabled(false);
});

• Use a binding expression that is {{::yourModel}}

• Reduce the number of watchers

• Avoid using ng-repeat in infinite scroll loading. For solutions, please refer to this

  article

• 使用性能测试的小工具去挖掘你的angular性能问题，我们可以使用简单的console.time()也可以借助开发者工具以及Batarang

console.time("TimerName");
//your code
console.timeEnd("TimerName");

9. 你认为在Angular中使用jQuery好么？

这是一个开放性的问题，尽管网上会有很多这样的争论，但是普遍还是认为这并不是一个特别好的尝试。其实当我们学习Angular的时候，我们应该做到从0去接受angular的思想，数据绑定，使用angular自带的一些api，合理的路由组织和，写相关指令和服务等等。angular自带了很多api可以完全替代掉jquery中常用的api，我们可以使用angular.element，$http,$timeout,ng-init等。

我们不妨再换个角度，如果业务需求，而对于一个新人（比较熟悉jQuery）的话，或许你引入jQuery可以让它在解决问题，比如使用插件上有更多的选择，当然这是通过影响代码组织来提高工作效率，随着对于angular理解的深入，在重构时会逐渐摒弃掉当初引入jquery时的一些代码。(?Po主就是这样的人，希望不要被嘲笑，业务却是赶着走)

所以我觉得两种框架说完全不能一起用肯定是错的，但是我们还是应该尽力去遵循angular的设计。

10. 如何进行angular的单元测试

我们可以使用karam＋jasmine 进行单元测试,我们通过ngMock引入angular app然后自行添加我们的测试用例。
一段简单的测试代码：

describe('calculator', function () {

  beforeEach(module('calculatorApp'));

  var $controller;

  beforeEach(inject(function(_$controller_){
    $controller = _$controller_;
  }));

  describe('sum', function () {
        it('1 + 1 should equal 2', function () {
            var $scope = {};
            var controller = $controller('CalculatorController', { $scope: $scope });
            $scope.x = 1;
            $scope.y = 2;
            $scope.sum();
            expect($scope.z).toBe(3);
        });    
    });

});

关于测试，大家可以看下使用karma进行angular测试

除了Karam , Angular.js团队推出了一款e2e(end-to-end)的测试框架protractor

参考

• 11 Essential AngularJS Interview Questions

• 11 Tips to Improve AngularJS Performance

• AngularJS: My solution to the ng-repeat performance problem

• 29 AngularJS Interview Questions – Can You Answer Them All?

• The Digest Loop and $apply

• What is the difference between '@' and '=' in directive scope

• Angular compile

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