如何检查通过rest参数传递的对象是null还是undefined？

Question

function extend(...args) , if I run the function and pass a null object in this

function extend({}) , how to check if this is null or undefined.

Input: const first = { x: 2, y: 3}; const second = { a: 70, x: 4, z: 5 }; const third = { x: 0, y: 9, q: 10 }; const firstSecondThird = extend(first, second, third);

Expected Output: { x: 2, y: 3, a: 70, z: 5, q: 10 } I must also check that for each entry in ...args , that it is an object and not undefined; if any are undefined, it must throw an error. I must also check that there are at least 2 arguments.

Answer 1

• You can check length of Object.keys to check {} . As Boolean({}) is true .
• Use includes() to check whether args contain null or undefined
• Use some() and typeof to check if all the elements of array are object .
• You what you don't want you properties to be overwritten if its occurs twice. Then you can you reverse()

 function extend(...args){ if(args.length < 2) throw ("Length is less than 2"); if(!args.some(arg => typeof arg !== "object" || Object.keys(arg).length >=2 )) throw ("Arguments contain something other than object") if(args.includes(undefined) || args.includes(null)) throw ("Arguments contain null or undefined"); else return Object.assign(...args.reverse()) } const first = { x: 2, y: 3}; const second = { a: 70, x: 4, z: 5 }; const third = { x: 0, y: 9, q: 10 }; const firstSecondThird = extend(first, second, third); console.log(firstSecondThird) console.log(extend({})); console.log(extend(1,2,3, undefined)); console.log(extend(1,2,3, null)); console.log(extend([]));

The above all if statements can be combined as one statement.

Answer 2

you can implement this for your expected output..

 const first = { x: 2, y: 3 }; const second = { a: 70, x: 4, z: 5 }; const third = { x: 0, y: 9, q: 10 }; const fourth = undefined; const firstSecondThird = extend(first, second, third, fourth); function extend (...args) { let result = Object.assign({}, ...args.reverse()); if (result.length < 2) throw ("Length is less than 2"); if (args.includes(undefined) || args.includes(null)) throw ("args contains undefined") return result; } console.log(firstSecondThird)

 const first = { x: 2, y: 3 }; const second = { a: 70, x: 4, z: 5 }; const third = { x: 0, y: 9, q: 10 }; const firstSecondThird = extend(first, second, third); function extend (...args) { let result = Object.assign({}, ...args.reverse()); if (result.length < 2) throw ("Length is less than 2"); if (args.includes(undefined) || args.includes(null)) throw ("args contains undefined") return result; } console.log(firstSecondThird)