I'm attempting to implement optional chaining with an array instead of an object but I'm unsure how to proceed:
Here's my attempt at using it
myArray.filter(x => x.testKey === myTestKey)?[0]let x = {a: () => {}, b: null}
console.log(x?b());
However, I keep encountering a similar error - is there a way to utilize optional chaining with an array or a function?
If you want to implement optional chaining, remember to include a period (.) after the question mark (?) like this:
myArray.filter(x => x.testKey === myTestKey)?.[0]
For a hands-on demonstration, check out the Playground link
It's important to note that using just the question mark alone may confuse the compiler into thinking you're utilizing the conditional operator - which will result in an error if no colon is provided later in the code.
Optional chaining isn't exclusive to TypeScript; it has been incorporated as a finalized proposal even in plain JavaScript.
This feature can be applied not only with bracket notation as previously shown but also with dot notation for property access:
const obj = {
prop2: {
nested2: 'val2'
}
};
console.log(
obj.prop1?.nested1,
obj.prop2?.nested2
);In addition, optional chaining works seamlessly with function calls too:
const obj = {
fn2: () => console.log('fn2 running')
};
obj.fn1?.();
obj.fn2?.();After a quick search on the official documentation's what's new page, I stumbled upon this gem.
To properly handle arrays, simply add a . after the ? symbol.
For example:
myArray.filter(x => x.testKey === myTestKey)?.[0] // for objects
x?.() // for functions
Let me shed some light on a specific case related to my previous question.
myArray.filter(x => x.testKey === myTestKey)?[0]
This transpiles to:
const result = myArray.filter(x => x.testKey === myTestKey) ? [0] : ;
An error is thrown due to the missing code after : in the transpiled version, which is not desired.
Credit goes to Certain Performance's answer for introducing me to TypeScript, especially the useful tool available at https://www.typescriptlang.org/play/index.html.
When using ECMA 262 (2020) on Edge Chromium 84, I discovered that the Optional Chaining operator can be executed without the need for a TypeScript transpiler:
// All result are undefined
const a = {};
console.log(a?.b);
console.log(a?.["b-foo-1"]);
console.log(a?.b?.());
// Note that the following statements throw exceptions:
a?.(); // TypeError: a is not a function
a?.b(); // TypeError: a?.b is not a function
Running a function inside an object is not always necessary; you can also use optional chaining for this purpose. Here's an example:
someOperation?.();
If the function someOperation exists, it will be executed. Otherwise, the execution will be skipped without throwing an error.
This technique is especially handy when dealing with reusable components that may or may not have certain functions defined.
Despite understanding the correct syntax, the code remains puzzling to me.
The use of optional chaining in the provided code ensures that the result of
myArray.filter(x => x.testKey === myTestKey)null nor undefined, as confirmed by the TypeScript output. However, this precaution may not be necessary since the result of the filter method always yields an array. JavaScript does not throw "Array bounds exceeded" errors, thus accessing any index will simply return undefined if the element does not exist.
For further clarity, consider the following examples:
const myArray: string[] = undefined
console.log(myArray.filter(x => x)?.[0]) //throws Cannot read property 'filter' of undefined
// In this instance, the optional chaining protects against an undefined array
const myArray: string[] = undefined
console.log(myArray?.filter(x => x)[0]) //outputs "undefined"
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