lib/process_babel_presets.js
function isBuiltinPreset(name) {
	var isNpmPresetName = /^(?:babel-preset-)/;
	var availablePresets = babel.availablePresets || {};

	var shorthand = isNpmPresetName.test(name) ?
		name.replace("babel-preset-", "") :
		name;

	return !!availablePresets[shorthand];
}
function isBuiltinPreset(name) {
	var isNpmPresetName = /^(?:babel-preset-)/;
	var availablePresets = babel.availablePresets || {};

	var shorthand = isNpmPresetName.test(name) ?
		name.replace("babel-preset-", "") :
		name;

	return !!availablePresets[shorthand];
}
function isBuiltinPreset ( name ) { var isNpmPresetName = / ^(?:babel-preset-) / ; var availablePresets = babel . availablePresets || { } ; var shorthand = isNpmPresetName . test ( name ) ? name . replace ( "babel-preset-" , "" ) : name ; return ! ! availablePresets [ shorthand ] ; }
Whether the preset is built in babel-standalone

@param {string} name A preset path
@return {boolean} `true` if preset is builtin, `false` otherwise

Babel presets can be set using the following variations:

1) the npm preset name, which by convention starts with `babel-preset-`
2) A shorthand name, which is the npm name without the prefix
3) A path to where the preset is defined

babel-standalone registers the builtin presets using the shorthand version.
Whether the preset is built in babel - standalone