isabella232 / meteor-variable

Simple reactive variables that contain EJSON values.

variable

Simple reactive variables that contain EJSON values.

This package encapsulates a simple but common case for reactive dependencies: when you want to have a simple variable that contains an EJSON-compatible value, and you'd like that variable to be a reactive data source.

When set, the variable only triggers a reactive update if the new value is actually different than the old one.

var weather = new Variable("sunny");

// prints "weather: sunny" as the autorun runs for the first time.
Deps.autorun(function () {
  console.log("weather: ", weather());
});

weather.set("sunny");    // nothing printed, the value hasn't changed
weather.set("hailing");  // prints "weather: hailing"

Note that while variables are similar to Meteor’s Session object in that they provide a reactive data source, variables are not a complete Session replacement: variables are unnamed and aren’t persisted across hot code pushes like Session key/values are.

Version

1.0.0

Meteor linker supported: This implementation works with both pre-linker Meteor (0.6.4.1 and below) and the new "linker" version of Meteor (0.6.5-rc12 and above).

API

new Variable()

[new] Variable(initialValue)   Anywhere

Creates and returns a new variable. The JavaScript new keyword is optional.

Arguments

initialValue: EJSON-compatible value

The initial value for the variable.

variable()

variable()   Anywhere

Returns the current value of the variable. A reactive data source.

variable.set()

variable.set(value)   Anywhere

Sets the value of the value. Triggers a reactive update (invalidates dependent computations) if the new value is different than the old.

Arguments

value: EJSON-compatible value

The new value for the variable.

Using with isolateValue

The isolate-value package can be used to further isolate reactive updates, if needed.

var post = new Variable({title: "Greetings", status: "draft"});

function title() {
  return isolateValue(function() {
    return post().title;
  });
}

// does not trigger an invalidation of a computation using title()

post.set({title: "Greetings", status: "published"});

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