为什么我的函数总是返回未定义的？

Question

I have written a function to search in a nested object. The problem is that it returns undefined instead of the expected result, that is correctly logged in the console. Whats going on there?

 const in1 = [1, 2]; const in2 = [1, 2]; const vDOM = { 1: { ref: in1, children: { 2: { ref: in2, children: {} } } } } const findVDOMNode = function(instance, vDOM) { const keys = Object.keys(vDOM); const foundKey = keys.find(key => vDOM[key].ref === instance); //console.log(foundKey, vDOM, "FK"); if (!keys.length) { console.log('no keys'); return; } if (foundKey) { console.log('found', vDOM[foundKey]); return true; //vDOM[foundKey]; }; keys.map(key => findVDOMNode(instance, vDOM[key].children)); } console.log('res: ', findVDOMNode(in2, vDOM)); 

Live example: https://stackblitz.com/edit/js-dapzsy

Answer 1

Just add return at the end.

return keys.map(key =>
    findVDOMNode(instance, vDOM[key].children));

You could take the values of the object and check it against the instance. If an object is found, check the object as well. For iterating use some with short circuit, if the instance is found.

 const in1 = [1, 2], in2 = [1, 2], vDOM = { 1: { ref: in1, children: { 2: { ref: in2, children: {} } } } }, findVDOMNode = (instance, vDOM) => Object .values(vDOM) .some(v => v === instance || v && typeof v === 'object' && findVDOMNode(instance, v) ); console.log('res: ', findVDOMNode(in2, vDOM)); 

Answer 2

it looks like you are missing a return statement on the map in the last line of the function

 const in1 = [1, 2]; const in2 = [1, 2]; const vDOM = { 1: { ref: in1, children: { 2: { ref: in2, children: {} } } } } const findVDOMNode = function(instance, vDOM) { const keys = Object.keys(vDOM); const foundKey = keys.find(key => vDOM[key].ref === instance); //console.log(foundKey, vDOM, "FK"); if (!keys.length) { console.log('no keys'); return; } if (foundKey) { console.log('found', vDOM[foundKey]); return true; //vDOM[foundKey]; }; ///added this return statement return keys.map(key => findVDOMNode(instance, vDOM[key].children)); } console.log('res: ', findVDOMNode(in2, vDOM));