Holder.js 使用说明

http://www.javascriptoo.com/holder-js/readme

Installing

npm: npm install holderjs

Bower: bower install holderjs

RawGit: https://cdn.rawgit.com/imsky/holder/master/holder.js
cdnjs: http://cdnjs.com/libraries/holder
jsDelivr: http://www.jsdelivr.com/#!holder
Rails Assets: gem 'rails-assets-holderjs'

Meteor: meteor add imsky:holder

Composer: php composer.phar update imsky/holder

NuGet: Install-Package Holder.js

Usage

Include holder.js in your HTML:

<script src="holder.js"></script>

Holder will then process all images with a specific src attribute, like this one:

<img src="holder.js/300x200">

The above tag will render as a placeholder 300 pixels wide and 200 pixels tall.

To avoid console 404 errors, you can use data-src instead of src.

Programmatic usage

To programmatically insert a placeholder use the run() API:

var myImage = document.getElementById('myImage');

Holder.run({

images: myImage

});

Placeholder options

Placeholder options are set through URL properties, e.g. holder.js/300x200?x=y&a=b. Multiple options are separated by the & character.

theme: The theme to use for the placeholder. Example: holder.js/300x200?theme=sky

random: Use random theme. Example: holder.js/300x200?random=yes

bg: Background color. Example: holder.js/300x200?bg=2a2025

fg: Foreground (text) color. Example: holder.js/300x200?fg=ffffff

text: Custom text. Example: holder.js/300x200?text=Hello

size: Custom text size. Defaults to pt units. Example: holder.js/300x200?size=50

font: Custom text font. Example: holder.js/300x200?font=Helvetica

align: Custom text alignment (left, right). Example: holder.js/300x200?align=left

outline: Draw outline and diagonals for placeholder. Example: holder.js/300x200?outline=yes

lineWrap: Maximum line length to image width ratio. Example: holder.js/300x200?lineWrap=0.5

Themes

Holder includes support for themes, to help placeholders blend in with your layout.

There are 6 default themes: sky, vine, lava, gray, industrial, and social.

Customizing themes

Themes have 5 properties: foreground, background, size, font and fontweight. The size property specifies the minimum font size for the theme. The fontweight default value is bold. You can create a sample theme like this:

Holder.addTheme("dark", {

background: "#000",

foreground: "#aaa",

size: 11,

font: "Monaco",

fontweight: "normal"

});

If you have a group of placeholders where you'd like to use particular text, you can do so by adding a text property to the theme:

Holder.addTheme("thumbnail", { background: "#fff", text: "Thumbnail" });

Using custom themes

There are two ways to use custom themes with Holder:

Include theme at runtime to render placeholders already using the theme name

Include theme at any point and re-render placeholders that are using the theme name

The first approach is the easiest. After you include holder.js, add a script tag that adds the theme you want:

<script src="holder.js"></script>

<script>

Holder.addTheme("bright", {

background: "white", foreground: "gray", size: 12

});

</script>

The second approach requires that you call run after you add the theme, like this:

Holder.addTheme("bright", {background: "white", foreground: "gray", size: 12}).run();

Using custom themes and domain on specific images

You can use Holder in different areas on different images with custom themes:

<img data-src="example.com/100x100?theme=simple" id="new">

Holder.run({

domain: "example.com",

themes: {

"simple": {

background: "#fff",

foreground: "#000",

size: 12

}

},

images: "#new"

});

Inserting an image with custom theme

You can add a placeholder programmatically by chaining Holder calls:

Holder.addTheme("new", {

foreground: "#ccc",

background: "#000",

size: 10

}).addImage("holder.js/200x100?theme=new", "body").run();

The first argument in addImage is the src attribute, and the second is a CSS selector of the parent element.

Text

Holder automatically adds line breaks to text that goes outside of the image boundaries. If the text is so long it goes out of both horizontal and vertical boundaries, the text is moved to the top. If you prefer to control the line breaks, you can add \n to
the text property:

<img data-src="holder.js/300x200?text=Add \n line breaks \n anywhere.">

If you would like to disable line wrapping, set the nowrap option to true:

<img data-src="holder.js/300x200?text=Add \n line breaks \n anywhere.&nowrap=true">

Placeholders using a custom font are rendered using canvas by default, due to SVG's constraints on cross-domain resource linking. If you're using only locally available fonts, you can disable this behavior by setting noFontFallback to true in Holder.run options.
However, if you need to render a SVG placeholder using an externally loaded font, you have to use the object tag instead of the img tag and add a holderjs class to the appropriate link tags. Here's an example:

<head>

<link href="http://.../font-awesome.css" rel="stylesheet" class="holderjs">

</head>

<body>

<object data-src="holder.js/300x200?font=FontAwesome"></object>

Important: When testing locally, font URLs must have a http or https protocol defined.

Important: Fonts served from locations other than public registries (i.e. Google Fonts, Typekit, etc.) require the correct CORS headers to be set. See How to use CDN with Webfonts for more details.

<object> placeholders work like <img> placeholders, with the added benefit of their DOM being able to be inspected and modified. As with <img> placeholders, the data-src attribute is more reliable than the data attribute.

Fluid placeholders

Important: Percentages are specified with the p character, not with the % character.

Specifying a dimension in percentages creates a fluid placeholder that responds to media queries.

<img data-src="holder.js/100px75?theme=social">

By default, the fluid placeholder will show its current size in pixels. To display the original dimensions, i.e. 100%x75, set the textmode flag to literal like so: holder.js/100px75?textmode=literal.

Automatically sized placeholders

If you'd like to avoid Holder enforcing an image size, use the auto flag like so:

<img data-src="holder.js/200x200?auto=yes">

The above will render a placeholder without any embedded CSS for height or width.

To show the current size of an automatically sized placeholder, set the textmode flag to exact like so: holder.js/200x200?auto=yes&textmode=exact.

Preventing updates on window resize

Both fluid placeholders and automatically sized placeholders in exact mode are updated when the window is resized. To set whether or not a particular image is updated on window resize, you can use the setResizeUpdate method like so:

var img = $('#placeholder').get(0);

Holder.setResizeUpdate(img, false);

The above will pause any render updates on the specified image (which must be a DOM object).

To enable updates again, run the following:

Holder.setResizeUpdate(img, true);

This will enable updates and immediately render the placeholder.

Background placeholders

Holder can render placeholders as background images for elements with the holderjs class, like this:

#sample {background:url(?holder.js/200x200?theme=social) no-repeat}

<div id="sample" class="holderjs"></div>

The Holder URL in CSS should have a ? in front. Like in image placeholders, you can specify the Holder URL in a data-background-src attribute:

<div class="holderjs" data-background-src="?holder.js/300x200"></div>

Important: Make sure to define a height and/or width for elements with background placeholders. Fluid background placeholders are not yet supported.

Runtime settings

Holder provides several options at runtime that affect the process of image generation. These are passed in through Holder.run calls.

domain: The domain to use for image generation. Default value: holder.js.

dataAttr: The HTML attribute used to define a fallback to the native src attribute. Default value: data-src.

renderer: The renderer to use. Options available: svg, canvas. Default value: svg.

images: The CSS selector used for finding img tags. Default value: img.

objects: The CSS selector used for finding object placeholders. Default value: object.

bgnodes: The CSS selector used for finding elements that have background palceholders. Default value: body .holderjs.

stylenodes: The CSS selector used for finding stylesheets to import into SVG placeholders. Default value: head link.holderjs.

Using custom settings on load

You can prevent Holder from running its default configuration by executing Holder.run with your custom settings right after including holder.js. However, you'll have to execute Holder.run again to render any placeholders that use the default configuration.

Using with lazyload.js

Holder is compatible with lazyload.js and works with both fluid and fixed-width images. For best results, run .lazyload({skip_invisible:false}).

Using with Angular.js

You can use Holder in Angular projects with ng-holder.

Using with Meteor

Because Meteor includes scripts at the top of the document by default, the DOM may not be fully available when Holder is called. For this reason, place Holder-related code in a "DOM ready" event listener.

Browser support

Chrome

Firefox 3+

Safari 4+

Internet Explorer 9+ (with partial support for 6-8)

Opera 12+

Android (with fallback)