esformatter-collapse-objects

esformatter plugin for conditionally collapsing object and array literals.

Features

• Conditionally formats literals on a single line, while leaving others expanded
• Respects your original esformatter whitespace settings
• Conditions include a max line-length, a max number of keys/elements in the literal, a max depth of the literal (when it contains other objects or arrays), or when it contains complex expressions like inline function expressions.

Usage

install it:

npm install esformatter-collapse-objects

and something like this to your esformatter config file:

{
  "plugins": [
    "esformatter-collapse-objects"
  ]
}

Important: Update your esformatter config

This plugin works by relying on esformatter expanding the relevant expressions, and conditionally collapsing them back down to a single line. Therefore, you need to have esformatter expand them in the first place (esformatter defaults to expanding object literals, but not array literals).

Add the following to your esformatter config when collapsing arrays:

"lineBreak": {
  "before": {
    "ArrayExpressionClosing": 1
  },
  "after": {
    "ArrayExpressionOpening": 1,
    "ArrayExpressionComma": 1
  }
},

Since expressions were collapsed, you might be surprised that some appear as {a:b,c:d}. This is because esformatter defaults are tuned toward expanded expressions. Try merging the following into your config for whitespace before each property in an object:

{
  "whiteSpace": {
    "before": {
      "PropertyName": 1
    }
}

Options

The following is the default configuration for the plugin, which can be reproduced and modified in your .esformatter config:

{
  "collapseObjects": {
    "ObjectExpression": {
      "maxLineLength": 80,
      "maxKeys": 3,
      "maxDepth": 2,
      "forbidden": [
        "FunctionExpression"
      ]
    },
    "ArrayExpression": {
      "maxLineLength": 80,
      "maxKeys": 3,
      "maxDepth": 2,
      "forbidden": [
        "FunctionExpression"
      ]
    }
  }
}

Options map esprima AST Node types (in this case both ObjectExpression and ArrayExpression) to their respective options, just like indentation in esformatter.

Set either expression's value to -1 to opt out of collapsing those nodes.

maxLineLength (int)

If the literal exceeds a certain number of columns collapsed, it will not be collapsed.

Use a maxLineLength of -1 to ignore this option.

forbidden (Array)

You can also avoid collapsing literals under certain conditions like a maximum number of keys, or when they contain other nodes like FunctionExpression.

[function foo() { return 'bar' }]

for example, could never occur since FunctionExpression is forbidden when trying to collapse a literal if this is set.

Use a forbidden of [] to ignore this option.

maxDepth (int)

You can also limit the depth of nested literals. All literals begin at a depth of 1, and for performance reasons setting a maxDepth of greater than 3 is ignored. For example, {foo: { bar: 'baz' }} has a depth of two and would be collapsed if the maxDepth is 2 or greater.

Use a maxDepth of -1 to opt out of this functionality.

JavaScript API

Register the plugin and call esformatter like so:

// register plugin
esformatter.register(require('esformatter-collapse-objects'));
// pass options as second argument
var output = esformatter.format(str, options);

License

Released under the MIT License.

Credits

Huge thanks to Jörn Zaefferer, who published an MIT-licensed gist which serves as the foundation for this module.