How to prevent babel transform operator 'typeof' in JS - babeljs

Question

I develope a JS SDK with ES6 grammar. The file size of the SDK is about 8Kb. After compile it with babel, size of SDK is about 20Kb. I find that babel transforms operator typeof with a helper "babel-runtime/helpers/typeof", which increase my SDK's size. If I don't use typeof in my SDK, the file size of my SDK is about 7Kb.
_validateCallback(fnName, arg) {
if (typeof arg !== 'function') {
throw new TypeError(`[${fnName}]'s arguments[0] must be a function, but get a ${typeof arg}`);
}
}
The detail of my .babelrc:
{
"presets": [
[
"env",
{
"targets": {
"browsers": [
"last 2 versions",
"ie >= 9"
]
}
}
],
"stage-2"
],
"plugins": [
"transform-runtime"
]
}
The devDependencies of package.json
{
"babel-cli": "^6.26.0",
"babel-core": "^6.26.3",
"babel-loader": "^7.1.5",
"babel-plugin-transform-runtime": "^6.23.0",
"babel-preset-env": "^1.7.0",
"babel-preset-stage-2": "^6.24.1",
"webpack": "^4.37.0",
"webpack-cli": "^3.3.6"
}
The detail of my webpack.config.js
{
mode: 'production',
entry: './main.js',
output: {
path: path.resolve(__dirname, 'dist'),
filename: 'botapp-sdk.' + PACKAGE.version + '.js',
library: 'BotApp',
libraryTarget: 'var',
},
plugins: [
new webpack.HashedModuleIdsPlugin(),
new webpack.optimize.ModuleConcatenationPlugin(),
new webpack.BannerPlugin(PACKAGE.name + ' - ' + PACKAGE.version),
],
module: {
rules: [
{
test: /\.js$/,
exclude: /node_modules/,
use: 'babel-loader'
}
]
}
}
I need to prevent babel to transform 'typeof', so that I can reduce file size of my SDK.
Is there any way to prevent babel transform operator typeof ?

Answer 1

I have been find a way to solve the question:
## -8,7 +8,10 ##
"last 2 versions",
"ie >= 9"
]
- }
+ },
+ "exclude": [
+ "transform-es2015-typeof-symbol"
+ ]
}
],
"stage-2"
The detail of exclude see: https://babeljs.io/docs/en/babel-preset-env#exclude

Answer 2

I have the same issue. I have no idea, what is the problem with typeof, as it seem to be a day one feature of ES. There is some issue with Symbol object, but I didn't find any article highlighting the problem.
Anyways, the possible solution is just to drop typeof:
!(arg instanceOf Function)
Also, a solid workaround is an oldstyle typechecker:
Object.prototype.toString.call(alert) === '[object Function]'
My prefered way is just to check if call exists:
args.call && console.log('OK')
The benefit of typeof is that it works fine with undeclared variables.
In your case, it doesn't matter, because arg is declared as a function argument. In case it's not, you should use try/catch to avoid possible ReferenceError.