将变量设置为“this"是否有功能目的? [英] Is there a functional purpose for setting a variable to 'this'?

问题描述

例如，有时当我查看其他人的代码时，他们会使用 var self = this; 或者在 jquery 中例如使用 var $self = $(this);

As in, sometimes when I look at code by other people, they will go var self = this; or in jquery for example, go var $self = $(this);

这样做有什么特别的原因吗?

is there a particular reason for doing so?

推荐答案

正如其他人提到的，如果你想在另一个函数中使用它，你可以将一个变量设置为 $(this).

As others have mentioned, you could set a variable to $(this) if you wish to use it in another function.

实际示例是执行与页面上的事件相关的 ajax 调用.使用 JQuery:

On practical example would be when doing an ajax call tied to an event on the page. Using JQuery:

<script>

        $(document).on("click", ".mySelector", function () {
            // Where we are in the click event, $(this) refers to whatever
            // element has a class of mySelector that was clicked
            var self = $(this);
            theDiv.html('');
            $.ajax({
                cache: false,
                type: "GET",
                url: "/SomeAjaxMethod",
                data: { },
                success: function (data) {
                    // Trying to access $(this) here will return undefined, as
                    // we are technically in the callback method
                    // Where our event is based on a class, there is likely more
                    // than one element on the page with the class, so it would be
                    // difficult to get the exact element again without some other code
                    self.html(data);
                },
                error: function (xhr, ajaxOptions, thrownError) {
                    alert("Ajax failed.")
                }
            }); // end ajax call
        }); // end on mySelector class click
</script>

或:

<script>
    $(document).ready(function () {
        $('.foo').click(function () {
            var self = $(this);           // Whatever element that was clicked with foo class
            $('.bar').each(function () {
                var bar = $(this);        // Current iteration of bar element in the loop
                var baz = self;           // self is still the initial value, but $(this) is not
            }); // end bar loop
        }); // end foo click
    }); // end doc ready
</script>

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