binding.startParent()

This method checks whether the binding should listen to the parent; if it should and it hasn’t already started listening, then it will start listening to the parent and update the child in the queue provided when the binding was initialized.

Usually you would want to start the child and parent listeners at the same time, but calling startParent first and then calling start later is useful when the child value hasn’t been initialized, as is the case with can-stache-bindings where we create the binding, read the parentValue, then create the child with all of the parent values.

The example below shows a hypothetical scenario (with a hypothetical API, can-value.returnedBy) in which the child’s value isn’t really created until after startParent has been called:

import Bind from "can-bind";
import DefineMap from "can-define/map/map";
import value from "can-value";

let childMap;// Will be set later
const parentMap = new DefineMap({parentProp: "parent value"});

// Create the binding
const binding = new Bind({
  child: value.returnedBy(function() {
    return childMap.childProp;
  }),
  parent: value.bind(parentMap, "parentProp")
});

// Turn on just the parent listener
binding.startParent();

// Now we can get the parent’s value to create the child
childMap = new DefineMap({
  childProp: binding.parentValue
});

// Now turn on the child listener
binding.start();