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Read & Write Properties

Nodes have properties to which one can read or write a value. It is the most common and basic task when developing a node. Fortunately, it is also incredibly easy.

Read a Property Value​

The simpiliest way to read data from a property is to use context.get('<property_name>').

 

properties.yaml
count:
  datatype: number
  default: 1
main.js
console.log('Count is', context.get('count'));
output
Count is 1

Changing a Property​

Writing values to a property is also fairly simple, but for more complex values may require a bit more. Primitive datatypes such as text, number, and boolean are easy. More complex datatype like arrays and object require a little more thought, although it depends largely on what is being accomplished.

Writing a Value​

The recommended and simpiliest way to write a value to a property is to use context.set('{property_name}', {value}). This write operation will completely replace the prior value. For non-primitive values like arrays and object this may be less desireable; in those cases a mutate may be more appropriate. Additionally, some time you need to see the prior value as part of the change operation; in this case you can use the update context function instead of set.

 

main.js
context.set('count', 2); // set value to a property
output
Count before write is 1
Count after write is 2

Update Values​

Optionally, if you need to reference the prior value as part of writing a value, it is better to use context.update(). context.update() has the form context.update(<property name>, <update function>).

 

main.js
context.update('count', (prev) => prev + 1);

Update Object Values​

If you are working with objects, you can also do fine-grain updates using context.mutate. Fine-grain mutations are preferred in reactive systems because we can reactively update the other connected properties in a fine-grained manner; meaning we can only update the part that changed, as opposed to the whole object. context.mutate() has the form context.mutate(<property name>, <mutate function>). Here's an example usage:

 

main.js
context.mutate('obj', (obj) => {
  obj.list[0] = '123';
  obj.list.push(456);
});