What you can do is check whether you props is defined initially or not by checking if nextProps.blog.content is undefined or not since your body is nested inside it like
componentWillReceiveProps(nextProps) {
if(nextProps.blog.content !== undefined && nextProps.blog.title !== undefined) {
console.log("new title is", nextProps.blog.title);
console.log("new body content is", nextProps.blog.content["body"]);
this.setState({
title: nextProps.blog.title,
body: nextProps.blog.content["body"]
})
}
}
You need not use type to check for undefined, just the strict operator !== which compares the value by their type as well as value
In order to check for undefined, you can also use the typeof operator like
typeof nextProps.blog.content != "undefined"
What you can do is check whether you props is defined initially or not by checking if nextProps.blog.content is undefined or not since your body is nested inside it like
componentWillReceiveProps(nextProps) {
if(nextProps.blog.content !== undefined && nextProps.blog.title !== undefined) {
console.log("new title is", nextProps.blog.title);
console.log("new body content is", nextProps.blog.content["body"]);
this.setState({
title: nextProps.blog.title,
body: nextProps.blog.content["body"]
})
}
}
You need not use type to check for undefined, just the strict operator !== which compares the value by their type as well as value
In order to check for undefined, you can also use the typeof operator like
typeof nextProps.blog.content != "undefined"
I was face same problem ..... And I got solution by using typeof()
if (typeof(value) !== 'undefined' && value != null) {
console.log('Not Undefined and Not Null')
} else {
console.log('Undefined or Null')
}
You must have to use typeof() to identified undefined
Videos
In TypeScript 2, you can use the undefined type to check for undefined values.
If you declare a variable as:
let uemail : string | undefined;
Then you can check if the variable uemail is undefined like this:
if(uemail === undefined)
{
}
From Typescript 3.7 on, you can also use nullish coalescing:
let x = foo ?? bar();
Which is the equivalent for checking for null or undefined:
let x = (foo !== null && foo !== undefined) ?
foo :
bar();
https://www.typescriptlang.org/docs/handbook/release-notes/typescript-3-7.html#nullish-coalescing
While not exactly the same, you could write your code as:
var uemail = localStorage.getItem("useremail") ?? alert('Undefined');
Hello guys, i need your help, i would like to know which you think is a better approach:
1 --------------------------------------------
const {content} = props;
if(content !== "undefined"){
//code
}
2 --------------------------------------------
const {content = null} = props;
if(!content){
//code
}
You can use Optional Chaining instead.
If the language is not null or undefined (nullish) it will access the property or method you want otherwise it will return undefined
If you're damn sure about language that it can't be null or undefined then use ! operator (non-null assertion operator) and rewrite your code like this:
import { filter } from 'lodash';
...
return filter(channels, ({
language
}: Channels) => {
return language!.toLowerCase().includes(selectedCategory);
});
Or You can use Optional Chaining instead.
Update: For simplicity, I replicated the original error with simpler code.
Update 2: I got around this by using a type guard for T. Thank u/ritajalilip for the suggestion. I still think Typescript should handle this better though.
As you can see on the screenshot, inside the if statement I'm asserting that x is not undefined. However Typescript is failing to acknowledge and still thinks that x can be undefined.
Any idea of what's going on?
This code do not work at all, but not sure why.
type IsUndefined<T> = T extends undefined ? 1 : 0;
For example:
type IsTypeUndefined = IsUndefined<number | undefined>; // This returns: 1 | 0
Is there a way for check if a type is undefined in a conditional?
// typescript
<span>
{day.date.split('-').pop().replace(/^0/, '')} // Object is possibly undefined
</span>
I thought I could just put some ? in there, but I can't get the error to go away.