Proposal for extensible input/field types from the JSON block definition

Problem statement

Adding or modifying an input or field type in the block JSON definition requires customisation of the Blockly.Block.prototype.interpolate_ function - adding or changing a case in the switch statement … https://github.com/google/blockly/blob/master/core/block.js#L1143

Proposal

I’d like to suggest replacing the switch with a object of input/field handlers, into which we can add new types or override existing types.

Blockly.Block.jsonInputTypes = {
  input_value: function(element) {
    return this.appendValueInput(element['name']);
  },
  ...
};

Blockly.Block.jsonFieldTypes = {
  field_label: function(element) {
    return Blockly.Block.newFieldLabelFromJson_(element);
  },
  ...
};

and replace the switch with:

var inputType = Blockly.Block.jsonInputTypes[element['type']]
var fieldType = Blockly.Block.jsonFieldTypes[element['type']]

if (inputType) {
  input = inputType.call(this, element)
} else if (fieldType) {
  field = fieldType.call(this, element)
}

// The input/field fn may return null so it falls back to the 'alt' definition

if (!input && !field && element['alt']) {
  element = element['alt'];
  altRepeat = true;
}

if its something that you think could be accepted into the codebase I’d be more than happy to prepare a PR and sign the CLA.

[RoboErikG]

I have a preference for API calls so that it’s less painful if we need to change the implementation in the future.

[jollytoad]

@rachel-fenichel thanks for the quick turn around on #1592, now that’s merged I’ve submitted a proper PR for this ^