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144 lines
4.2 KiB
Markdown
144 lines
4.2 KiB
Markdown
## Writing plugins ##
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All you need to do to make a new plugin is creating an init function
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and a set of options (if needed), stuffing it into an object and
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putting it in the $.plot.plugins array. For example:
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```js
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function myCoolPluginInit(plot) {
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plot.coolstring = "Hello!";
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};
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$.plot.plugins.push({ init: myCoolPluginInit, options: { ... } });
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// if $.plot is called, it will return a plot object with the
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// attribute "coolstring"
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```
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Now, given that the plugin might run in many different places, it's
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a good idea to avoid leaking names. The usual trick here is wrap the
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above lines in an anonymous function which is called immediately, like
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this: (function () { inner code ... })(). To make it even more robust
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in case $ is not bound to jQuery but some other Javascript library, we
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can write it as
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```js
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(function ($) {
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// plugin definition
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// ...
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})(jQuery);
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```
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There's a complete example below, but you should also check out the
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plugins bundled with Flot.
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## Complete example ##
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Here is a simple debug plugin which alerts each of the series in the
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plot. It has a single option that control whether it is enabled and
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how much info to output:
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```js
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(function ($) {
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function init(plot) {
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var debugLevel = 1;
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function checkDebugEnabled(plot, options) {
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if (options.debug) {
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debugLevel = options.debug;
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plot.hooks.processDatapoints.push(alertSeries);
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}
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}
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function alertSeries(plot, series, datapoints) {
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var msg = "series " + series.label;
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if (debugLevel > 1) {
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msg += " with " + series.data.length + " points";
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alert(msg);
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}
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}
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plot.hooks.processOptions.push(checkDebugEnabled);
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}
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var options = { debug: 0 };
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$.plot.plugins.push({
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init: init,
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options: options,
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name: "simpledebug",
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version: "0.1"
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});
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})(jQuery);
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```
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We also define "name" and "version". It's not used by Flot, but might
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be helpful for other plugins in resolving dependencies.
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Put the above in a file named "jquery.flot.debug.js", include it in an
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HTML page and then it can be used with:
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```js
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$.plot($("#placeholder"), [...], { debug: 2 });
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```
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This simple plugin illustrates a couple of points:
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- It uses the anonymous function trick to avoid name pollution.
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- It can be enabled/disabled through an option.
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- Variables in the init function can be used to store plot-specific
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state between the hooks.
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The two last points are important because there may be multiple plots
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on the same page, and you'd want to make sure they are not mixed up.
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## Shutting down a plugin ##
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Each plot object has a shutdown hook which is run when plot.shutdown()
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is called. This usually mostly happens in case another plot is made on
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top of an existing one.
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The purpose of the hook is to give you a chance to unbind any event
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handlers you've registered and remove any extra DOM things you've
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inserted.
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The problem with event handlers is that you can have registered a
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handler which is run in some point in the future, e.g. with
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setTimeout(). Meanwhile, the plot may have been shutdown and removed,
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but because your event handler is still referencing it, it can't be
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garbage collected yet, and worse, if your handler eventually runs, it
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may overwrite stuff on a completely different plot.
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## Some hints on the options ##
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Plugins should always support appropriate options to enable/disable
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them because the plugin user may have several plots on the same page
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where only one should use the plugin. In most cases it's probably a
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good idea if the plugin is turned off rather than on per default, just
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like most of the powerful features in Flot.
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If the plugin needs options that are specific to each series, like the
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points or lines options in core Flot, you can put them in "series" in
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the options object, e.g.
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```js
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var options = {
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series: {
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downsample: {
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algorithm: null,
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maxpoints: 1000
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}
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}
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}
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```
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Then they will be copied by Flot into each series, providing default
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values in case none are specified.
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Think hard and long about naming the options. These names are going to
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be public API, and code is going to depend on them if the plugin is
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successful.
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