Obj 没有密钥时的处理

Question

How can we make obj handle/execute a function when it does not have a key?

for example

 const abc = { a: () => console.log('key exist') } console.log(abc.a()) console.log (abc.c())

Here, console.log(abc.a()) will print key exist but I want if someone who tries to access a key which does not exist then it should run a different a function.

I want it to handle this thing at object level ie I can do if (abc[c]) and then do something else but since I am going to call this obj from many different place and I don't want to have if-else condition.

Is this possible?

Answer 1

Perhaps this?

 const abc = { a: () => console.log('key exist'), notfound: () => console.log('key does\'t exit') } console.log(abc.a()) console.log ((abc?.c||abc.notfound)())

Answer 2

You can check if the property c exists on the object first. i also added a check to see if it's indeed a function.

 const abc = { a: () => console.log('key exist') } console.log(abc.a()); console.log (abc.c && typeof abc.c === 'function'? abc.c(): "not found");

Answer 3

You could use Nullish coalescing operator to solve your issue:

The nullish coalescing operator (??) is a logical operator that returns its right-hand side operand when its left-hand side operand is null or undefined, and otherwise returns its left-hand side operand.

More info see MDN Web Docs - Nullish Coalescing Operator .

Nulish coalescing operator is part of the ECMAScript 2020 specification. Lookup can i use for browser support details.

 //With external default (() => { const abc = { a: () => console.log('key exist') } const myFunction = abc.c?? (() => console.log("key doesn't exist")) myFunction(); })(); //With internal default (() => { const abc = { a: () => console.log('key exist'), default: () => console.log("key doesn't exist") } const myFunction = abc.c?? abc.default myFunction(); })();

If your project needs to support older browser, use Binary logical operator OR ( || ) instead:

The logical OR (||) operator (logical disjunction) for a set of operands is true if and only if one or more of its operands is true.

If a value can be converted to true, the value is so-called truthy. If a value can be converted to false, the value is so-called falsy.

Expressions that can be converted to false

• null
• NaN
• 0
• empty string ( "" or '' or `` )
• undefined

More info see MDN Web Docs - Logical OR .

 //With external default (() => { const abc = { a: () => console.log('key exist') } const myFunction = abc.c || (() => console.log("key doesn't exist")) myFunction(); })(); //With internal default (() => { const abc = { a: () => console.log('key exist'), default: () => console.log("key doesn't exist") } const myFunction = abc.c || abc.default myFunction(); })();

Answer 4

I you want to avoid the use of if/else every time you need to run a function that may or may not exist, you can create a global function:

 const run = (cb) => typeof cb === "function"? cb(): () => {} const abc = { a: () => console.log('key exist') } console.log(run(abc.a)) console.log(run(abc.c))