undefined

问题 I work in an area where memory utilization is very important to us, as we don't run on your classic web browsers / hardware. We use null quite a lot in our application, one thing that has not been clear to me is if null takes up more space than assigning a variable to undefined. Do we know if one or the other is more costly on memory usage? Thanks for help! 回答1: As you can see in this jsperf test, null seems to be slightly faster in the chrome (V8, just like nodejs) which might indicate it

问题 I work in an area where memory utilization is very important to us, as we don't run on your classic web browsers / hardware. We use null quite a lot in our application, one thing that has not been clear to me is if null takes up more space than assigning a variable to undefined. Do we know if one or the other is more costly on memory usage? Thanks for help! 回答1: As you can see in this jsperf test, null seems to be slightly faster in the chrome (V8, just like nodejs) which might indicate it

问题 The result that's logged to the console ( answer ) is the correct one, but it's coming out of the function as undefined. What is going on? let sorted = []; function reset(){ sorted = []; } function sort(list) { let least = list[0]; for (let i = 0; i < list.length; i++){ if (list[i] < least ){ least = list[i]; } } sorted.push(least); list.splice(list.indexOf(least),1); if (list[0] !== undefined){ sort(list) } else { let answer = sorted; reset(); console.log(answer); return answer; } } let

问题 The result that's logged to the console ( answer ) is the correct one, but it's coming out of the function as undefined. What is going on? let sorted = []; function reset(){ sorted = []; } function sort(list) { let least = list[0]; for (let i = 0; i < list.length; i++){ if (list[i] < least ){ least = list[i]; } } sorted.push(least); list.splice(list.indexOf(least),1); if (list[0] !== undefined){ sort(list) } else { let answer = sorted; reset(); console.log(answer); return answer; } } let

问题 Codeflow is- I am checking if an entry called listobject exists in the AsyncStorage. If it doesn't exist, then, I create an object, add few attributes and set the store. I get the store to obj as I have to compare in the next if condition. If the listobject entry already exists(2nd time), then, it directly comes to the 2nd block, and compares. (The reason I get values to obj in 1st step is because I can have a common obj.data.isdirty condition. Here is my code- AsyncStorage.getItem(

问题 I am a C++ programmer starting with PHP. I find that I lose most of the debugging time (and my selfesteem!) due to undefined variables. From what I know, the only way to deal with them is to watch the output at execution time. Are other strategies to notice these faults earlier (something like with C++ that a single compile gives you all the clues you need)? 回答1: This is a common complaint with PHP. Here are some ideas: Use a code analysis tool. Many IDEs such as NetBeans will help also. Just

问题 This works fine var isRenderer = typeof process !== "undefined" && process.type === "renderer"; I don't like having those typeof checks all over my code, so I tried writing a helper function. But using it causes a reference error to be thrown var isRenderer = !isUndefined(process) && process.type === "renderer"; function isUndefined(val) { return typeof val === "undefined"; } I have two questions: Why does the helper function I wrote not work? Is it possible to write a helper function to

问题 I was not clear in my problem description. Let me try again. NB. This is a problem common to my production, staging, and development sites (not just to my delevlopment site as the commenters seem to have thought). NB. This problem occurs bowsing with Chrome and not with Firefox. The problem occurs at the site home page: http://www.example.com (or with "/index.php appended"). The page loads successfully, but the Console pannel of Chrome's Developer Tools shows a 404 error. The message reads

问题 I've been searching or a solution to my problem, but none of the aswers I find are useful. I try to make an automatic form that submits itself when the page loads. $(document).getElementById('ticketCount').submit(function(){ $.ajax({ method:$(this).attr('method'), url:$(this).attr('action'), data:$(this).serialize() }) .done(function(data){ $('#ticketCount').html(data); }) .error(function(data){ console.log(data); }); }); My console tells me that: "Uncaught TypeError: undefined is not a

问题 I am trying to store some images on my Node.JS server and read it from Angular client with the following codes: image.ts: export class Image { fieldname: string; originalname: string; encoding: string; mimetype: string; destination: string; filename: string; path: string; size: number; } image.service.ts: export class ImagesService { constructor(private http: HttpClient, private processHTTPMsgService: ProcessHTTPMsgService) { } getImages(): Observable<Image[]> { return this.http.get<Image[]>