Property '...' has no initializer and is not definitely assigned in the constructor
JavascriptAngularTypescriptJavascript Problem Overview
in my Angular app i have a component:
import { MakeService } from './../../services/make.service';
import { Component, OnInit } from '@angular/core';
@Component({
selector: 'app-vehicle-form',
templateUrl: './vehicle-form.component.html',
styleUrls: ['./vehicle-form.component.css']
})
export class VehicleFormComponent implements OnInit {
makes: any[];
vehicle = {};
constructor(private makeService: MakeService) { }
ngOnInit() {
this.makeService.getMakes().subscribe(makes => { this.makes = makes
console.log("MAKES", this.makes);
});
}
onMakeChange(){
console.log("VEHICLE", this.vehicle);
}
}
but in the "makes" property I have a mistake. I dont know what to do with it...
Javascript Solutions
Solution 1 - Javascript
Just go to tsconfig.json and set
"strictPropertyInitialization": false
to get rid of the compilation error.
Otherwise you need to initialize all your variables which is a little bit annoying
Solution 2 - Javascript
I think you are using the latest version of TypeScript. Please see the section "Strict Class Initialization" in the link
.
There are two ways to fix this:
A. If you are using VSCode you need to change the TS version that the editor use.
B. Just initialize the array when you declare it
makes: any[] = [];
or inside the constructor:
constructor(private makeService: MakeService) {
// Initialization inside the constructor
this.makes = [];
}
Solution 3 - Javascript
It is because TypeScript 2.7 includes a strict class checking where all the properties should be initialized in the constructor. A workaround is to add
the !
as a postfix to the variable name:
makes!: any[];
Solution 4 - Javascript
We may get the message Property has no initializer and is not definitely assigned in the constructor
when adding some configuration in the tsconfig.json
file so as to have an Angular project compiled in strict mode:
"compilerOptions": {
"strict": true,
"noImplicitAny": true,
"noImplicitThis": true,
"alwaysStrict": true,
"strictNullChecks": true,
"strictFunctionTypes": true,
"strictPropertyInitialization": true,
Indeed the compiler then complains that a member variable is not defined before being used.
For an example of a member variable that is not defined at compile time, a member variable having an @Input
directive:
@Input() userId: string;
We could silence the compiler by stating the variable may be optional:
@Input() userId?: string;
But then, we would have to deal with the case of the variable not being defined, and clutter the source code with some such statements:
if (this.userId) {
} else {
}
Instead, knowing the value of this member variable would be defined in time, that is, it would be defined before being used, we can tell the compiler not to worry about it not being defined.
The way to tell this to the compiler is to add the ! definite assignment assertion
operator, as in:
@Input() userId!: string;
Now, the compiler understands that this variable, although not defined at compile time, shall be defined at run-time, and in time, before it is being used.
It is now up to the application to ensure this variable is defined before being used.
As an an added protection, we can assert the variable is being defined, before we use it.
We can assert the variable is defined, that is, the required input binding was actually provided by the calling context:
private assertInputsProvided(): void {
if (!this.userId) {
throw (new Error("The required input [userId] was not provided"));
}
}
public ngOnInit(): void {
// Ensure the input bindings are actually provided at run-time
this.assertInputsProvided();
}
Knowing the variable was defined, the variable can now be used:
ngOnChanges() {
this.userService.get(this.userId)
.subscribe(user => {
this.update(user.confirmedEmail);
});
}
Note that the ngOnInit
method is called after the input bindings attempt, this, even if no actual input was provided to the bindings.
Whereas the ngOnChanges
method is called after the input bindings attempt, and only if there was actual input provided to the bindings.
Solution 5 - Javascript
Go to your tsconfig.json
file and change the property:
"noImplicitReturns": false
and then add
"strictPropertyInitialization": false
under "compilerOptions"
property.
Your tsconfig.json
file should looks like:
{
...
"compilerOptions": {
....
"noImplicitReturns": false,
....
"strictPropertyInitialization": false
},
"angularCompilerOptions": {
......
}
}
>Hope this will help !!
> Good Luck
Solution 6 - Javascript
The error is legitimate and may prevent your app from crashing. You typed makes
as an array but it can also be undefined.
You have 2 options (instead of disabling the typescript's reason for existing...):
1. In your case the best is to type makes
as possibily undefined.
makes?: any[]
// or
makes: any[] | undefined
So the compiler will inform you whenever you try to access to makes
that it could be undefined.
Otherwise, if the // <-- Not ok
lines below were executed before getMakes
finished or if getMakes
failed, your app would crash and a runtime error would be thrown. That's definitely not what you want.
makes[0] // <-- Not ok
makes.map(...) // <-- Not ok
if (makes) makes[0] // <-- Ok
makes?.[0] // <-- Ok
(makes ?? []).map(...) // <-- Ok
2. You can assume that it will never fail and that you will never try to access it before initialization by writing the code below (risky!). So the compiler won't take care about it.
makes!: any[]
More specifically,
Your design could be better. Defining a local and mutable variable is not a good practice. You should manage data storage inside your service:
- firstly to be nullsafe,
- secondly to be able to factorise a lot of code (including typing, loading state and errors)
- finally to avoid mulitple and useless reftech.
The exemple below try to show this but I didn't tested it and it could be improved:
type Make = any // Type it
class MakeService {
private readonly source = new BehaviorSubject<Make[] | undefined>(undefined);
loading = false;
private readonly getMakes = (): Observable<Make[]> => {
/* ... your current implementation */
};
readonly getMakes2 = () => {
if (this.source.value) {
return this.source.asObservable();
}
return new Observable(_ => _.next()).pipe(
tap(_ => {
this.loading = true;
}),
mergeMap(this.getMakes),
mergeMap(data => {
this.source.next(data);
return data;
}),
tap(_ => {
this.loading = false;
}),
catchError((err: any) => {
this.loading = false;
return throwError(err);
}),
);
};
}
@Component({
selector: 'app-vehicle-form',
template: `
<div *ngIf="makeService.loading">Loading...</div>
<div *ngFor="let vehicule of vehicules | async">
{{vehicle.name}}
</div>
`,
styleUrls: ['./vehicle-form.component.css']
})
export class VehicleFormComponent implements OnInit {
constructor(public makeService: MakeService) {}
readonly makes = this.makeService.getMakes2().pipe(
tap(makes => console.log('MAKES', makes))
);
readonly vehicules = this.makes.pipe(
map(make => make/* some transformation */),
tap(vehicule => console.log('VEHICLE', vehicule)),
);
ngOnInit() {
this.makes.subscribe(makes => {
console.log('MAKES', makes);
});
}
}
Solution 7 - Javascript
Update for 2021 :
> there is property like "strictPropertyInitialization"
Just go to tsconfig.json and set
"strict": false
to get rid of the compilation error.
Otherwise you need to initialize all your variables which is a little bit annoying.
reason behind this error is :
- typescript is a kind of more Secure lang as compare to javascript.
- although this security is enhance by enabling strict feature .So every time when you initialize a variable typescript wants them to assign a value.
Solution 8 - Javascript
You either need to disable the --strictPropertyInitialization
that
Sajeetharan referred to, or do something like this to satisfy the initialization requirement:
makes: any[] = [];
Solution 9 - Javascript
You can also do the following if you really don't want to initialise it.
makes?: any[];
Solution 10 - Javascript
If you want to initialize an object based on an interface you can initialize it empty with following statement.
myObj: IMyObject = {} as IMyObject;
Solution 11 - Javascript
Put a question (?) mark after makes variable.
makes?: any[];
vehicle = {};
constructor(private makeService: MakeService) { }
It should now works. I'm using angular 12 and it works on my code.
Solution 12 - Javascript
As of TypeScript 2.7.2, you are required to initialise a property in the constructor if it was not assigned to at the point of declaration.
If you are coming from Vue, you can try the following:
-
Add
"strictPropertyInitialization": true
to your tsconfig.json -
If you are unhappy with disabling it you could also try this
makes: any[] | undefined
. Doing this requires that you access the properties with null check (?.
) operator i.e.this.makes?.length
-
You could as well try
makes!: any[];
, this tells TS that the value will be assigned at runtime.
Solution 13 - Javascript
Get this error at the time of adding Node in my Angular project -
> TSError: ? Unable to compile TypeScript: (path)/base.api.ts:19:13 - error TS2564: Property 'apiRoot Path' has no initializer and is not definitely assigned in the constructor. > > private apiRootPath: string;
Solution -
Added "strictPropertyInitialization": false
in 'compilerOptions' of tsconfig.json.
my package.json -
"dependencies": {
...
"@angular/common": "~10.1.3",
"@types/express": "^4.17.9",
"express": "^4.17.1",
...
}
Solution 14 - Javascript
A batter approach would be to add the exclamation mark to the end of the variable for which you are sure that it shall not be undefined or null, for instance you are using an ElementRef which needs to be loaded from the template and can't be defined in the constructor, do something like below
class Component {
ViewChild('idname') variable! : ElementRef;
}
Solution 15 - Javascript
Solution 16 - Javascript
if you don't want to change your tsconfig.json, you can define your class like this:
class Address{
street: string = ''
}
or, you may proceed like this as well:
class Address{
street!: string
}
by adding an exclamation mark "!" before your variable name, Typescript will be sure that this variable is not null or undefined
Solution 17 - Javascript
there are many solutions
> demo code
class Plant {
name: string;
// ❌ Property 'name' has no initializer and is not definitely assigned in the constructor.ts(2564)
}
solutions
- add 'undefined' type
class Plant {
name: string | undefined;
}
- add definite assignment assertion
class Plant {
name!: string;
}
- declare with init value
class Plant {
name: string = '';
}
- use the constructor with an init value
class Plant {
name: string;
constructor() {
this.name = '';
}
}
- use the constructor and init value by params
class Plant {
name: string;
constructor(name: string) {
this.name = name ?? '';
}
}
- shorthand of the
5
class Plant {
constructor(public name: string = name ?? '') {
//
}
}
tsconfig.json
> not recommended
{
"compilerOptions": {
+ "strictPropertyInitialization": false,
- "strictPropertyInitialization": true,
}
}
refs
https://www.typescriptlang.org/docs/handbook/2/classes.html#--strictpropertyinitialization
Solution 18 - Javascript
When you upgrade using [email protected] , its compiler strict the rules follows for array type declare inside the component class constructor.
For fix this issue either change the code where are declared in the code or avoid to compiler to add property "strictPropertyInitialization": false in the "tsconfig.json" file and run again npm start .
Angular web and mobile Application Development you can go to www.jtechweb.in
Solution 19 - Javascript
Another way to fix in the case when the variable must remain uninitialized (and it is dealt with at the run time) is to add undefined
to the type (this is actually suggested by VC Code). Example:
@Input() availableData: HierarchyItem[] | undefined;
@Input() checkableSettings: CheckableSettings | undefined;
Depending on actual usage, this might lead to other issues, so I think the best approach is to initialize the properties whenever possible.
Solution 20 - Javascript
Can't you just use a Definite Assignment Assertion? (See https://www.typescriptlang.org/docs/handbook/release-notes/typescript-2-7.html#definite-assignment-assertions)
i.e. declaring the property as makes!: any[];
The ! assures typescript that there definitely will be a value at runtime.
Sorry I haven't tried this in angular but it worked great for me when I was having the exact same problem in React.
Solution 21 - Javascript
a new version of typescript has introduced strick class Initialization, that is means by all of the properties in your class you need to initialize in the constructor body, or by a property initializer. check it in typescript doccumntation to avoid this you can add (! or ?) with property
make!: any[] or make? : any[]
otherwise, if you wish to remove strick class checking permanently in your project you can set strictPropertyInitialization": false in tsconfig.json file
> "compilerOptions": { .... "noImplicitReturns": false, .... "strictPropertyInitialization": false },
Solution 22 - Javascript
Add these two line on the tsconfig.json
"noImplicitReturns": true,
"strictPropertyInitialization": false,
and make sure strict is set to true
Solution 23 - Javascript
change the
fieldname?: any[];
to this:
fieldname?: any;
Solution 24 - Javascript
This has been discussed in Angular Github at https://github.com/angular/angular/issues/24571
I think this is what everyone will move to
quote from https://github.com/angular/angular/issues/24571#issuecomment-404606595
For angular components, use the following rules in deciding between:
a) adding initializer
b) make the field optional
c) leave the '!'
If the field is annotated with @input - Make the field optional b) or add an initializer a).
If the input is required for the component user - add an assertion in ngOnInit and apply c.
If the field is annotated @ViewChild, @ContentChild - Make the field optional b).
If the field is annotated with @ViewChildren or @ContentChildren - Add back '!' - c).
Fields that have an initializer, but it lives in ngOnInit. - Move the initializer to the constructor.
Fields that have an initializer, but it lives in ngOnInit and cannot be moved because it depends on other @input fields - Add back '!' - c).
Solution 25 - Javascript
Property '...' has no initializer and is not definitely assigned in the constructor error fix in Angular
Solution 1: Disable strictPropertyInitialization flag
The simple way to fix this error in Angular applications is to disable --strictPropertyInitialization flag in typescript compiler options in tsconfig.json file.
"compilerOptions": {
///
,
"strictPropertyInitialization":false
}
Solution 2: Adding undefined type to the property
It’s ok to have an undefined property.
So while declaring variable add undefined type to the property.
employees: Employee[];
//Change to
employees : Employee[] | undefined;
Solution 3: Add definite assignment assertion to property
If you know that we will assign the property in later point in time.
It’s better to add definite assignment assertion to the property. i.e., employees.
employees!: Employee[];
Solution 4: Add initializer to property
Another way to make this type error go away is to add an explicit initializer to the property.
employees: Employee[] = [];
Solution 5: Assignment in the Constructor
Otherwise, we can assign some default value to the property in the constructor.
employees: Employee[];
constructor() {
this.employees=[];
}
Solution 26 - Javascript
You can declare property in constructor like this:
export class Test {
constructor(myText:string) {
this.myText= myText;
}
myText: string ;
}
Solution 27 - Javascript
JUST go to the tsconfig.ts and add "strictPropertyInitialization": false, into the compilerOptions Object .
- if it doesn't solve yet, kindly re-open your Code Editor.
EXAMPLE:
"compilerOptions" : {
"strictPropertyInitialization": false,
}
Solution 28 - Javascript
Comment the //"strict": true
line in tsconfig.json file.
Solution 29 - Javascript
You can also add @ts-ignore to silence the compiler only for this case:
//@ts-ignore
makes: any[];
Solution 30 - Javascript
Next to variables "?" You can fix it by putting it.
Example:
--------->id?:number --------->name?:string