了解JavaScript中的HTML字符串转义

Question

Hey i was just going though this plugin code online HERE:

$("#filer_input2").filer({
        limit: null,
        maxSize: null,
        extensions: null,
        changeInput: '<div class="jFiler-input-dragDrop"><div class="jFiler-input-inner"><div class="jFiler-input-icon"><i class="icon-jfi-cloud-up-o"></i></div><div class="jFiler-input-text"><h3>Drag&Drop files here</h3> <span style="display:inline-block; margin: 15px 0">or</span></div><a class="jFiler-input-choose-btn blue">Browse Files</a></div></div>',
        showThumbs: true,
        theme: "dragdropbox",
        templates: {
            box: '<ul class="jFiler-items-list jFiler-items-grid"></ul>',
            item: '<li class="jFiler-item">\
                        <div class="jFiler-item-container">\
                            <div class="jFiler-item-inner">\
                                <div class="jFiler-item-thumb">\
                                    <div class="jFiler-item-status"></div>\
                                    <div class="jFiler-item-info">\
                                        <span class="jFiler-item-title"><b title="{{fi-name}}">{{fi-name | limitTo: 25}}</b></span>\
                                        <span class="jFiler-item-others">{{fi-size2}}</span>\
                                    </div>\
                                    {{fi-image}}\
                                </div>\
                                <div class="jFiler-item-assets jFiler-row">\
                                    <ul class="list-inline pull-left">\
                                        <li>{{fi-progressBar}}</li>\
                                    </ul>\
                                    <ul class="list-inline pull-right">\
                                        <li><a class="icon-jfi-trash jFiler-item-trash-action"></a></li>\
                                    </ul>\
                                </div>\
                            </div>\
                        </div>\
                    </li>',
            itemAppend: '<li class="jFiler-item">\
                            <div class="jFiler-item-container">\
                                <div class="jFiler-item-inner">\
                                    <div class="jFiler-item-thumb">\
                                        <div class="jFiler-item-status"></div>\
                                        <div class="jFiler-item-info">\
                                            <span class="jFiler-item-title"><b title="{{fi-name}}">{{fi-name | limitTo: 25}}</b></span>\
                                            <span class="jFiler-item-others">{{fi-size2}}</span>\
                                        </div>\
                                        {{fi-image}}\
                                    </div>\
                                    <div class="jFiler-item-assets jFiler-row">\
                                        <ul class="list-inline pull-left">\
                                            <li><span class="jFiler-item-others">{{fi-icon}}</span></li>\
                                        </ul>\
                                        <ul class="list-inline pull-right">\
                                            <li><a class="icon-jfi-trash jFiler-item-trash-action"></a></li>\
                                        </ul>\
                                    </div>\
                                </div>\
                            </div>\
                        </li>',
            progressBar: '<div class="bar"></div>',
            itemAppendToEnd: false,
            removeConfirmation: true,
            _selectors: {
                list: '.jFiler-items-list',
                item: '.jFiler-item',
                progressBar: '.bar',
                remove: '.jFiler-item-trash-action'
            }
        },
        dragDrop: {
            dragEnter: null,
            dragLeave: null,
            drop: null,
        },
        uploadFile: {
            url: "./php/upload.php",
            data: null,
            type: 'POST',
            enctype: 'multipart/form-data',
            beforeSend: function(){},
            success: function(data, el){
                var parent = el.find(".jFiler-jProgressBar").parent();
                el.find(".jFiler-jProgressBar").fadeOut("slow", function(){
                    $("<div class=\"jFiler-item-others text-success\"><i class=\"icon-jfi-check-circle\"></i> Success</div>").hide().appendTo(parent).fadeIn("slow");    
                });
            },
            error: function(el){
                var parent = el.find(".jFiler-jProgressBar").parent();
                el.find(".jFiler-jProgressBar").fadeOut("slow", function(){
                    $("<div class=\"jFiler-item-others text-error\"><i class=\"icon-jfi-minus-circle\"></i> Error</div>").hide().appendTo(parent).fadeIn("slow");    
                });
            },
            statusCode: null,
            onProgress: null,
            onComplete: null
        },
        files: null,
        addMore: false,
        clipBoardPaste: true,
        excludeName: null,
        beforeRender: null,
        afterRender: null,
        beforeShow: null,
        beforeSelect: null,
        onSelect: null,
        afterShow: null,
        onRemove: function(itemEl, file, id, listEl, boxEl, newInputEl, inputEl){
            var file = file.name;
            $.post('./php/remove_file.php', {file: file});
        },
        onEmpty: null,
        options: null,
        captions: {
            button: "Choose Files",
            feedback: "Choose files To Upload",
            feedback2: "files were chosen",
            drop: "Drop file here to Upload",
            removeConfirmation: "Are you sure you want to remove this file?",
            errors: {
                filesLimit: "Only {{fi-limit}} files are allowed to be uploaded.",
                filesType: "Only Images are allowed to be uploaded.",
                filesSize: "{{fi-name}} is too large! Please upload file up to {{fi-maxSize}} MB.",
                filesSizeAll: "Files you've choosed are too large! Please upload files up to {{fi-maxSize}} MB."
            }
        }
    });

I know that the above is quite a wall of code , so let me narrow down on my difficulty:

itemAppend: '<li class="jFiler-item">\
                            <div class="jFiler-item-container">\
                                <div class="jFiler-item-inner">\
                                    <div class="jFiler-item-thumb">\
                                        <div class="jFiler-item-status"></div>\
                                        <div class="jFiler-item-info">\
                                            <span class="jFiler-item-title"><b title="{{fi-name}}">{{fi-name | limitTo: 25}}</b></span>\
                                            <span class="jFiler-item-others">{{fi-size2}}</span>\
                                        </div>\
                                        {{fi-image}}\
                                    </div>\
                                    <div class="jFiler-item-assets jFiler-row">\
                                        <ul class="list-inline pull-left">\
                                            <li><span class="jFiler-item-others">{{fi-icon}}</span></li>\
                                        </ul>\
                                        <ul class="list-inline pull-right">\
                                            <li><a class="icon-jfi-trash jFiler-item-trash-action"></a></li>\
                                        </ul>\
                                    </div>\
                                </div>\
                            </div>\
                        </li>',

why are all those escape characters doing at the end of the html elements IE the \\ ??? can somebody explain ?

Thanks.

Answer 1

Normal JavaScript string literals cannot have unescaped newlines in them:

// Syntax error
var str = "This is
a test";

With the backslash escaping the newline, you can have a line break without using a close quote and + :

// Escaping the newline makes it valid
var str = "This is\
a test";

The newline will not be in the string (but all the leading whitespace at the beginning of the next line will be).

Example:

 var str = "this is\\ a test"; console.log(JSON.stringify(str)); 

Answer 2

The \\ allows to define multiline strings in javascript.

For example:

var s = 'foo \
bar';

is the same as:

var s = 'foo bar';

It can be practical when you have long strings like the one in your example and it avoids the need of closing the string literal and concatenating it with another one.

Answer 3

Those back-slashes are for escaping new-lines, as mentioned in other answers.

However, since JavaScript ES-2015 you could use another type of string, which doesn't need the newline to be escaped. Those strings should be surrounded with ` .

 var multiline = `I am multiline`; console.log(multiline); 

Note that any type of indentation will be included in the string as excessive spacing, so be careful with it:

 function test(){ return `I am multiline`; } console.log(test());