ca18ea5e79
* Re-add optional chaining delete * Move exec tests next to output tests * Forgot to commit these
@babel/plugin-proposal-optional-chaining
The Optional Chaining Operator allows you to handle properties of deeply nested objects without worrying about undefined intermediate objects.
Example
Accessing deeply nested properties
const obj = {
foo: {
bar: {
baz: 42,
},
},
};
const baz = obj?.foo?.bar?.baz; // 42
const safe = obj?.qux?.baz; // undefined
// Optional chaining and normal chaining can be intermixed
obj?.foo.bar?.baz; // Only access `foo` if `obj` exists, and `baz` if
// `bar` exists
Calling deeply nested functions
const obj = {
foo: {
bar: {
baz() {
return 42;
},
},
},
};
const baz = obj?.foo?.bar?.baz(); // 42
const safe = obj?.qux?.baz(); // undefined
const safe2 = obj?.foo.bar.qux?.(); // undefined
const willThrow = obj?.foo.bar.qux(); // Error: not a function
// Top function can be called directly, too.
function test() {
return 42;
}
test?.(); // 42
exists?.(); // undefined
Constructing deeply nested classes
const obj = {
foo: {
bar: {
baz: class {
},
},
},
};
const baz = new obj?.foo?.bar?.baz(); // baz instance
const safe = new obj?.qux?.baz(); // undefined
const safe2 = new obj?.foo.bar.qux?.(); // undefined
const willThrow = new obj?.foo.bar.qux(); // Error: not a constructor
// Top classes can be called directly, too.
class Test {
}
new Test?.(); // test instance
new exists?.(); // undefined
Installation
npm install --save-dev @babel/plugin-proposal-optional-chaining
Usage
Via .babelrc (Recommended)
.babelrc
{
"plugins": ["@babel/plugin-proposal-optional-chaining"]
}
Via CLI
babel --plugins @babel/plugin-proposal-optional-chaining script.js
Via Node API
require("@babel/core").transform("code", {
plugins: ["@babel/plugin-proposal-optional-chaining"]
});
Options
loose
boolean, defaults to false.
When true, this transform will pretend document.all does not exist,
and perform loose equality checks with null instead of string equality checks
against both null and undefined.
Example
In
foo?.bar;
Out (loose === true)
foo == null ? void 0 : foo.bar;
Out (loose === false)
foo === null || foo === void 0 ? void 0 : foo.bar;