/Meteor 1.3


Documentation of ReactiveVar, a simple reactive variable package.

To use ReactiveVar, add the reactive-var package to your project by running in your terminal:

meteor add reactive-var

new ReactiveVar(initialValue, [equalsFunc])
import { ReactiveVar } from 'meteor/reactive-var' (reactive-var/reactive-var.js, line 37)

Constructor for a ReactiveVar, which represents a single reactive variable.


initialValue Any

The initial value to set. equalsFunc is ignored when setting the initial value.

equalsFunc Function

Optional. A function of two arguments, called on the old value and the new value whenever the ReactiveVar is set. If it returns true, no set is performed. If omitted, the default equalsFunc returns true if its arguments are === and are of type number, boolean, string, undefined, or null.

A ReactiveVar holds a single value that can be get and set, such that calling set will invalidate any Computations that called get, according to the usual contract for reactive data sources.

A ReactiveVar is similar to a Session variable, with a few differences:

  • ReactiveVars don’t have global names, like the “foo” in Session.get("foo"). Instead, they may be created and used locally, for example attached to a template instance, as in: this.foo.get().

  • ReactiveVars are not automatically migrated across hot code pushes, whereas Session state is.

  • ReactiveVars can hold any value, while Session variables are limited to JSON or EJSON.

An important property of ReactiveVars — which is sometimes a reason for using one — is that setting the value to the same value as before has no effect; it does not trigger any invalidations. So if one autorun sets a ReactiveVar, and another autorun gets the ReactiveVar, a re-run of the first autorun won’t necessarily trigger the second. By default, only primitive values are compared this way, while calling set on an argument that is an object (not a primitive) always counts as a change. You can configure this behavior using the equalsFunc argument.


Returns the current value of the ReactiveVar, establishing a reactive dependency.


Sets the current value of the ReactiveVar, invalidating the Computations that called get if newValue is different from the old value.


newValue Any

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