Babel plugin for unassert: Encourages programming with assertions by providing tools to compile them away.

babel-plugin-unassert removes assertions on build. So you can use assertions to declare preconditions, postconditions and invariants.

• unassert: Encourages programming with assertions by providing tools to compile them away.
• unassertify: Browserify transform for unassert
• webpack-unassert-loader: Webpack loader for unassert
• gulp-unassert: Gulp plugin for unassert
• unassert-cli: CLI for unassert

$ npm install --save-dev babel-plugin-unassert

For Babel 5 or lower, you need to use the 1.2.x release of babel-plugin-unassert.

$ npm install --save-dev babel-plugin-unassert@1.2.0

{
  "presets": [
    ...
  ],
  "env": {
    "production": {
      "plugins": [
        "babel-plugin-unassert"
      ]
    }
  }
}

$ babel /path/to/src/target.js > /path/to/build/target.js

$ babel --plugins babel-plugin-unassert /path/to/src/target.js > /path/to/build/target.js

or shortly,

$ babel --plugins unassert /path/to/src/target.js > /path/to/build/target.js

var babel = require('babel-core');
var jsCode = fs.readFileSync('/path/to/src/target.js');
var transformed = babel.transform(jsCode, {
    presets: [...],
    plugins: ['babel-plugin-unassert']
});
console.log(transformed.code);

For given math.js below,

'use strict';
var assert = require('assert');
function add (a, b) {
    console.assert(typeof a === 'number');
    assert(!isNaN(a));
    assert.equal(typeof b, 'number');
    assert.ok(!isNaN(b));
    return a + b;
}

Run babel with --plugins unassert to transform code.

$ babel --plugins unassert /path/to/demo/math.js > /path/to/build/math.js

You will see assert calls and declarations disappear.

'use strict';
function add(a, b) {
    return a + b;
}

babel-plugin-unassert supports ES6 module syntax and power-assert.

with .babelrc,

{
  "presets": [
    ...
  ],
  "env": {
    "development": {
      "presets": [
        "babel-preset-power-assert"
      ]
    },
    "production": {
      "plugins": [
        "babel-plugin-unassert"
      ]
    }
  }
}

production code below

import assert from 'assert';
class Calc {
    add (a, b) {
        assert(!(isNaN(a) || isNaN(b)));
        assert(typeof a === 'number');
        assert(typeof b === 'number');
        return a + b;
    }
}

becomes

'use strict';
class Calc {
    add(a, b) {
        return a + b;
    }
}

in production, and produces power-assert messages like

AssertionError:   # example.js:5
  assert(!(isNaN(a) || isNaN(b)))
         | |     |  |  |     |
         | |     |  |  true  NaN
         | false 3  true
         false

in development.

Assertion expressions are removed when they match patterns below. In other words, babel-plugin-unassert removes assertion calls that are compatible with Node.js standard assert API (and console.assert).

• assert(value, [message])
• assert.ok(value, [message])
• assert.equal(actual, expected, [message])
• assert.notEqual(actual, expected, [message])
• assert.strictEqual(actual, expected, [message])
• assert.notStrictEqual(actual, expected, [message])
• assert.deepEqual(actual, expected, [message])
• assert.notDeepEqual(actual, expected, [message])
• assert.deepStrictEqual(actual, expected, [message])
• assert.notDeepStrictEqual(actual, expected, [message])
• assert.fail([message])
• assert.fail(actual, expected, message, operator)
• assert.throws(block, [error], [message])
• assert.doesNotThrow(block, [message])
• assert.rejects(asyncFn, [error], [message])
• assert.doesNotReject(asyncFn, [error], [message])
• assert.ifError(value)
• console.assert(value, [message])

babel-plugin-unassert also removes assert variable declarations,

• var assert = require("assert")
• var assert = require("assert").strict
• var assert = require("power-assert")
• var assert = require("power-assert").strict
• import assert from "assert"
• import assert from "power-assert"

and assignments.

• assert = require("assert")
• assert = require("assert").strict
• assert = require("power-assert")
• assert = require("power-assert").strict

• Takuto Wada

We support Node under maintenance. In other words, we stop supporting old Node version when their maintenance ends.

This means that any other environment is not supported.

NOTE: If babel-plugin-unassert works in any of the unsupported environments, it is purely coincidental and has no bearing on future compatibility. Use at your own risk.

Licensed under the MIT license.