Error alert: The return type is missing in the array.map method

Question

Error alert: The return type is missing in the array.map method

After running ESLint on my TypeScript code, I received a warning that says:

"Missing return type on function.eslint(@typescript-eslint/explicit-function-return-type)". The warning specifically points to the lambda function within the map function.

private headerSelectionChanged(event): void {
    const { checked } = event.syntheticEvent.target;
    const newGridData = this.props.gridData.map(item => Object.assign(item, { selected: checked }));
    this.updateGridData(newGridData);
}

I am unsure what is causing this warning. Can you help me understand and fix it?

typescript eslint

Answer 1

Answer №1

The warning is appearing because your mapping function lacks a specified return type. To resolve this, you need to clearly define the return type in the following manner:

const newGridData = this.props.gridData.map((item): any => Object.assign(item, { selected: checked }));

Remember that Object.assign alters the target instead of duplicating it. If you wish to avoid modifying this.props.gridData, consider switching the positions of item and { selected: checked }:

const newGridData = this.props.gridData.map((item): any => Object.assign({ selected: checked }, item));

Alternatively, you can utilize the more recent object spread operator if it is supported:

const newGridData = this.props.gridData.map((item): any => ({ ...item, selected: checked }));

Answer 2

The warning is appearing because your mapping function lacks a specified return type. To resolve this, you need to clearly define the return type in the following manner:

const newGridData = this.props.gridData.map((item): any => Object.assign(item, { selected: checked }));

Remember that Object.assign alters the target instead of duplicating it. If you wish to avoid modifying this.props.gridData, consider switching the positions of item and { selected: checked }:

const newGridData = this.props.gridData.map((item): any => Object.assign({ selected: checked }, item));

Alternatively, you can utilize the more recent object spread operator if it is supported:

const newGridData = this.props.gridData.map((item): any => ({ ...item, selected: checked }));

Answer 3

Answer №2

Here is an example of how you can add types to your code:

private handleHeaderSelection(event: any): void {
const { checked } = event.syntheticEvent.target;
const updatedGridData = this.props.gridData.map((item: any) => Object.assign(item, { selected: checked }));
this.updateGridData(updatedGridData);

}

Answer 4

Here is an example of how you can add types to your code:

private handleHeaderSelection(event: any): void {
const { checked } = event.syntheticEvent.target;
const updatedGridData = this.props.gridData.map((item: any) => Object.assign(item, { selected: checked }));
this.updateGridData(updatedGridData);

}

Answer 5

Answer №3

It's a bit unclear what exactly "newGridData" is meant to represent. However, if we assume it is meant to be an array of objects with the type "GridData", then this code snippet might make more sense.

private headerSelectionChanged(event): void {
    const { checked } = event.syntheticEvent.target;
    const updatedGridDataArray = this.props.gridData.map<GridData>(item => Object.assign(item, { selected: checked }));
    this.updateGridData(updatedGridDataArray);
}

Answer 6

It's a bit unclear what exactly "newGridData" is meant to represent. However, if we assume it is meant to be an array of objects with the type "GridData", then this code snippet might make more sense.

private headerSelectionChanged(event): void {
    const { checked } = event.syntheticEvent.target;
    const updatedGridDataArray = this.props.gridData.map<GridData>(item => Object.assign(item, { selected: checked }));
    this.updateGridData(updatedGridDataArray);
}

Error alert: The return type is missing in the array.map method

Answer №1

Answer №2

Answer №3

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