Define UDF Helpers

Define it the same as babel-helpers.
The specifications are the same as for babel-helpers.

• They must have a default export, which is their entry-point.
• They can import other helpers, exclusively by using default imports.
• They can't have named exports.

@babel/helpers

Preparation

Be sure to write the following in the helpers file.
We will define helpers in the properties of helpers

import { helper } from 'babel-udf-helpers'

const helpers = Object.create(null);
export default helpers;

/** We will define the helper from here　*/

Syntax

The basic helper looks like this:

import { helper } from 'babel-udf-helpers'

const helpers = Object.create(null);
export default helpers;

/** We will define the helper from here　*/

helpers.<helperName> = helper`
  import <depHelperName1> from '<depHelperName1>'
  import <depHelperName2> from '<depHelperName2>'

  export default function _<helperName>(){
    <depHelperName1>();
    <depHelperName2>();
  };
`;

helpers.<depHelperName1> = helper`
  export default function _<depHelperName1>(){
    /** something */
  };
`;

helpers.<depHelperName2> = helper`
  export default function _<depHelperName2>(){
    /** something */
  };
`;

Example

Good

import { helper } from 'babel-udf-helpers'

const helpers = Object.create(null);
export default helpers;

helpers.customHelper = helper`
  import dep from "dependency";

  const foo = 2;

  export default function _customHelper(x) {
    return foo * dep() + x;
  };
`);

helpers.dependency = helper`
  export default function _dependency(){
    return 10;
  };
`;

Good Point

• helpers have a default export, which is their entry-point.
• You are importing other helpers exclusively by using the default import.
• You are not using named exports.

Bad

import { helper } from 'babel-udf-helpers'

const helpers = Object.create(null);
export default helpers;

helpers.customHelper = helper`
  import { dep } from 'dependency1';
  import dep2 from 'dependency2';

  const foo = 2;

  export default function _customHelper(x) {
    return foo * dep() + x;
  };
`);

helpers.dependency1 = helper`
  export default function _dependency1(){
    return {
      dep: function(){}
    }
  };
`;

helpers.dependency2 = helper`
  function _dependency2(){
    return {}
  };
`;

Bad Point

• Dependency import is not ImportDefaultDeclaration.
• You are importing a dependency that is not export default.

Best Practice

The most efficient way to understand helpers is to look at the code in @babel/helpers