Array is null in TypeScript

Question

I have this array:

productCarts: ProductModel[] = [];

And when I call this method in ngInit I have error Cannot read property 'length' of null:

addProductFromLocalStorage() {

            if (this.productCarts.length == 0) {
                this.productCarts  = this.fromLocalStorage;  
            } 
    }

Solution: My local storage return the null value and I hade exception.

give a bit more context. most likely you loose the this context when calling addProductFromLocalStorage(). — Stefan Vitz
– Stefan Vitz, Commented Nov 6, 2019 at 10:26

Aarsh · Accepted Answer · 2019-11-06 11:12:44Z

3

Try This :

addProductFromLocalStorage() {

            if (!this.productCarts || this.productCarts.length === 0) {
                this.productCarts  = this.fromLocalStorage;  
            } 
    }

!this.productCarts this will check null and undefined value

answered Nov 6, 2019 at 11:12

Aarsh

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1 Comment

SIn san sun Over a year ago

Thanks a lot. This is helpful.

AyushKatiyar · Accepted Answer · 2019-11-06 11:32:36Z

2

Try using,

addProductFromLocalStorage() {

        if (this.productCarts === undefined || this.productCarts.length == 0) {
            this.productCarts  = this.fromLocalStorage;  
        } 
}

The is error Cannot read property 'length' of null is encountered as this.productCarts has not been defined yet. You can also use the second approach as declare productCarts:ProductModel[] in the global execution context and in ngInit method mention this.productCarts = []. Using this approach would also help.

edited Nov 6, 2019 at 11:32

answered Nov 6, 2019 at 11:10

AyushKatiyar

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1 Comment

SIn san sun Over a year ago

Thanks a lot. This is helpful.

pegaltier · Accepted Answer · 2019-11-06 10:27:10Z

1

You can solve this issue with the latest Typescript 3.7 feature called optional chaining: https://devblogs.microsoft.com/typescript/announcing-typescript-3-7/#optional-chaining

answered Nov 6, 2019 at 10:27

pegaltier

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1 Comment

SIn san sun Over a year ago

I hade a problem because my local storage returns the null.

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