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Angularjs Expression-Expression

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Author: User
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Later, we will talk about angularjs DI (Dependency Injection). Here we will introduce the expression about angularjs. Expression refers to a small part of javascript code, which is usually used to bind binding. For example: {expression }}. In angularjs, $ parse service is used for parsing.

$ Parse usage: $ parse (expression );

The following expressions are valid expressions in angularjs:

Angularjs expression vs. javascript expression

Angularjs view expressions are a bit like javascript expressions, but they are not parsed and executed using javascript expressions eval (). The differences between them and javascript expressions are as follows:

Note: angularjs expressions can be parsed and executed using the $ eval () method.

 

Demo

Html:

 

 
 
    
  
  
  1. <!doctype html> 
    2. 
  
  
  2.  
    3. 
  
  
  3.  
    4. 
  
  4.  
    5. 
  
  
  5.  
    6. 
  
  6.  
    7. 
  
  
  7. <script src="http://code.angularjs.org/angular-1.0.2.min.js"></script> 
    8. 
  
  
  8.  
    9. 
  
  
  9. <script src="script.js"></script> 
    10. 
  
  
  10.  
    11. 
  
  
  11.  
    12. 
  
  12.  
    13. 
  
  
  13. <body> 
    14. 
  
  
  14.  
    15. 
  
  
  15. <div ng-controller="Cntl2" class="expressions"> 
    16. 
  
  
  16.  
    17. 
  
  
  17. Expression:  
    18. 
  
  
  18.  
    19. 
  
  
  19. <input type='text' ng-model="expr" size="80"/> 
    20. 
  
  
  20.  
    21. 
  
  
  21. <button ng-click="addExp(expr)">Evaluate</button> 
    22. 
  
  
  22.  
    23. 
  
  
  23. <ul> 
    24. 
  
  
  24.  
    25. 
  
  
  25. <li ng-repeat="expr in exprs"> 
    26. 
  
  
  26.  
    27. 
  
  
  27. [ <a href="" ng-click="removeExp($index)">X</a> ]  
    28. 
  
  
  28.  
    29. 
  
  
  29. <tt>{{expr}}</tt> =&gt; <span ng-bind="$parent.$eval(expr)"></span> 
    30. 
  
  
  30.  
    31. 
  
  
  31. </li> 
    32. 
  
  
  32.  
    33. 
  
  
  33. </ul> 
    34. 
  
  
  34.  
    35. 
  
  
  35. </div> 
    36. 
  
  
  36.  
    37. 
  
  
  37. </body> 
    38. 
  
  
  38.  
    39. 
  
  
  39.  
    40. 
  
  40.  
    41.

Js:

 
 
    
  
  
  1. function Cntl2($scope) {  
    2. 
  
  
  2.  
    3. 
  
  
  3. var exprs = $scope.exprs = [];  
    4. 
  
  
  4.  
    5. 
  
  
  5. $scope.expr = '3*10|currency';  
    6. 
  
  
  6.  
    7. 
  
  
  7. $scope.addExp = function(expr) {  
    8. 
  
  
  8.  
    9. 
  
  
  9. exprs.push(expr);  
    10. 
  
  
  10.  
    11. 
  
  
  11. };  
    12. 
  
  
  12.  
    13.

 

$ Scope. removeExp = function (index ){

Exprs. splice (index, 1 );

};

}

Jsfiddle Demo: http://jsfiddle.net/whitewolf/yduLt/1/

Attribute execution

All expression execution in angularjs depends on one action on the scope, which is different from the global scope of the window in javascript. if you want to reference a global window, this must be dependent on the DI feature referenced in the previous section $ window service. example:

Html:

 
 
    
  
  
  1. <!doctype html> 
    2. 
  
  
  2.  
    3. 
  
  
  3.  
    4. 
  
  4.  
    5. 
  
  
  5.  
    6. 
  
  6.  
    7. 
  
  
  7. <script src="http://code.angularjs.org/angular-1.0.2.min.js"></script> 
    8. 
  
  
  8.  
    9. 
  
  
  9. <script src="script.js"></script> 
    10. 
  
  
  10.  
    11. 
  
  
  11.  
    12. 
  
  12.  
    13. 
  
  
  13. <body> 
    14. 
  
  
  14.  
    15. 
  
  
  15. <div class="example2" ng-controller="Cntl1"> 
    16. 
  
  
  16.  
    17. 
  
  
  17. Name: <input ng-model="name" type="text"/> 
    18. 
  
  
  18.  
    19. 
  
  
  19. <button ng-click="greet()">Greet</button> 
    20. 
  
  
  20.  
    21. 
  
  
  21. </div> 
    22. 
  
  
  22.  
    23. 
  
  
  23. </body> 
    24. 
  
  
  24.  
    25. 
  
  
  25.  
    26. 
  
  26.  
    27.

Js:

 
 
    
  
  
  1. function Cntl1($window, $scope){  
    2. 
  
  
  2.  
    3. 
  
  
  3. $scope.name = 'World';  
    4. 
  
  
  4.  
    5. 
  
  
  5.    
    6. 
  
  
  6.  
    7. 
  
  
  7. $scope.greet = function() {  
    8. 
  
  
  8.  
    9. 
  
  
  9. ($window.mockWindow || $window).alert('Hello ' + $scope.name);  
    10. 
  
  
  10.  
    11. 
  
  
  11. }  
    12. 
  
  
  12.  
    13. 
  
  
  13. }  
    14. 
  
  
  14.  
    15.

Jsfiddle Demo: http://jsfiddle.net/whitewolf/MF2Ku/1/

Compatible execution

As mentioned above: angularjs expression computation is compatible with processing null and undefined, and will not throw any exception because it will handle the reality in view display, while javascript will throw the NullPointerExceptions exception. For example, expression

{A. B. c}. The javascript code with the same effect will be {(a |{}). B |{}). c }}. Uncontrolled Process

In angularjs expressions, there will be no conditions, loops, and throw control flow statements. Angularjs, as mvc or close to pm mode, requires that the presentation layer logic be included in the controller, rather than the view, and the view should be passive enough. In expression mode, we try our best to extract the unchanged presentation logic of the presentation layer and a variety of easy-to-change UI views to facilitate automated testing and building.

Filter Filters)

Data is only used as a persistence storage domain model presentation layer or actually a view model viewmodel). When presented to users, it is often more user-friendly, such as time, number, currency format localization,

For example, name | uppercase, 123 | number: 2, 3*10 | currency.

Filters supports chained writing. How to use a pipeline model in the same language as powershell or other operating system shell, such as value | filter1 | filter2.

 

For other resources, refer to other angularjs documents in this blog or official angularjs documents http://angularjs.org /.

This article is an English version of an article which is originally in the Chinese language on aliyun.com and is provided for information purposes only. This website makes no representation or warranty of any kind, either expressed or implied, as to the accuracy, completeness ownership or reliability of the article or any translations thereof. If you have any concerns or complaints relating to the article, please send an email, providing a detailed description of the concern or complaint, to info-contact@alibabacloud.com. A staff member will contact you within 5 working days. Once verified, infringing content will be removed immediately.

Related Keywords:
constant expression eval expression expression character glob expression regression expression switch expression expression true

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