为什么在 angular 指令 `ngForm` 中使用了 "preLink" 函数，而不是常规的 "postLink" 函数？

Question

里面angular.js，在ngForm(form)指令定义中，编译函数returns只有一个preLink函数。为什么应该是 preLink 而不是常见的 postLink?

以下代码来自angular.js master分支：

var formDirective = {
  name: 'form',
  restrict: isNgForm ? 'EAC' : 'E',
  controller: FormController,
  compile: function ngFormCompile(formElement) {
    // Setup initial state of the control
    formElement.addClass(PRISTINE_CLASS).addClass(VALID_CLASS);
    return {
      pre: function ngFormPreLink(scope, formElement, attr, controller) {
        // if `action` attr is not present on the form, prevent the default action (submission)
        if (!('action' in attr)) {
          // we can't use jq events because if a form is destroyed during submission the default
          // action is not prevented. see #1238
          //
          // IE 9 is not affected because it doesn't fire a submit event and try to do a full
          // page reload if the form was destroyed by submission of the form via a click handler
          // on a button in the form. Looks like an IE9 specific bug.
          var handleFormSubmission = function(event) {
            scope.$apply(function() {
            controller.$commitViewValue();
            controller.$setSubmitted();
          });
        event.preventDefault();
        };
        ...

Answer 1

pre-link 函数在任何 child 指令之前执行，因此它是准备任何数据以供 child 指令使用的好地方。我假设在这种情况下它会准备提交处理程序，以防 child 指令在其 post-link 函数中提交表单。

实际上 link 函数的执行顺序是：

parent pre-link
child pre-link
child post-link
parent post-link

为什么在 angular 指令 `ngForm` 中使用了 "preLink" 函数，而不是常规的 "postLink" 函数？

Why a "preLink" function is used in angular directive `ngForm`, instead of regular "postLink" function?

angularjs

angularjs-directive

angularjs-ng-form