prevState is a name that you have given to the argument passed to setState callback function. What it holds is the value of state before the setState was triggered by React; Since setState does batching, its sometimes important to know what the previous state was when you want to update the new state based on the previous state value. So … Read more
The issue could be with the response you are receiving from back-end. If it was working fine on the server then the problem could be with the response headers. Check the Access-Control-Allow-Origin (ACAO) in the response headers. Usually react’s fetch API will throw fail to fetch even after receiving response when the response headers’ ACAO and the … Read more
I am trying to run some ES6 code in my project but I am getting an unexpected token export error.
Generic answer This error is caused when you call a function that expects an Object as its argument, but pass undefined or null instead, like for example As that is usually by mistake, the solution is to check your code and fix the null/undefined condition so that the function either gets a proper Object, or does not get called at all. Answer specific to … Read more
Javascript is very flexible with regards to checking for “null” values. I’m guessing you’re actually looking for empty strings, in which case this simpler code will work: Which will check for empty strings (“”), null, undefined, false and the numbers 0 and NaN Please note that if you are specifically checking for numbers it is a common mistake to miss 0 with this method, … Read more
The best string format for string parsing is the date ISO format together with the JavaScript Date object constructor. Examples of ISO format: YYYY-MM-DD or YYYY-MM-DDTHH:MM:SS. But wait! Just using the “ISO format” doesn’t work reliably by itself. String are sometimes parsed as UTC and sometimes as localtime (based on browser vendor and version). The best practice should always … Read more
Do: using the identity operator (===), which doesn’t make any implicit type conversions when the compared variables have different types. Don’t: You should probably be cautious about using these two methods for your specific needs: Any string which isn’t the empty string will evaluate to true by using them. Although they’re the cleanest methods I can think of concerning … Read more
The difference is, as the docs say There is also $(document).on( “ready”, handler ), deprecated as of jQuery 1.8. This behaves similarly to the ready method but if the ready event has already fired and you try to .on( “ready” ) the bound handler will not be executed. Ready handlers bound this way are executed after any bound by the … Read more
It seems to me, this is a cross-domain issue since you’re not allowed to make a request to a different domain. You have to find solutions to this problem: – Use a proxy script, running on your server that will forward your request and will handle the response sending it to the browser Or – … Read more
className is used instead of class in JSX because class is a JavaScript keyword. All JSX gets turned into vanilla JavaScript. If you wrote class it would try to make a JavaScript class and not make an element that has a class. So, when you write react it looks like this. Then something like babel will take that code and turn it into vanilla JavaScript: … Read more