Why use variable names as keys in object properties instead of variable values?

Question

I'm trying to use a Record object where type TableId = string;. However, when I print the contents of the record object after setting the key/value pairs via setTableStateMap(map)... what I get is the object {id: {…}} instead of the value I passed to the 'id' variable.

// App.tsx------------------------------ ----------
React.useEffect(() => {
    setCallback((id: TableId, tableState: TableState) => {
        const map: Record<TableId, TableState> = { id: tableState };
        setTableStateMap(map);
    });
    

// Table Component----------------------------------
type TableId = string;
type Callback = (id: TableId, state: TableState) => void;
let callback: Callback;
export function setCallback(callbackInput: Callback) {
    callback = callbackInput;
}

let stateMap: Record<TableId, TableState> = {};
export function setTableStateMap(map: Record<TableId, TableState>) {
    stateMap = map;
}

interface TableProps {
    id?: TableId;
}

export const Table: React.FC<TableProps> = ({
    ID,
}) => {

    let tableState: TableState | undefined;
    if (id) {
        tableState = stateMap[id];
        // The key of stateMap is set to 'id', not the value of the variable id
        // {id: {…}}
    } else {
        tableState = undefined;
    }
};

Answer 1

When you create an object using curly braces like { id: tableState }, the string "id" is interpreted as a static key instead of the dynamic value of the id variable. You need to use computed property names in JavaScript/TypeScript. Computed property names allow you to use dynamic values ​​as keys when creating objects.

// App.tsx---------------------------------------
React.useEffect(() => {
    setCallback((id: TableId, tableState: TableState) => {
        const map: Record<TableId, TableState> = { [id]: tableState }; // 在这里使用计算属性名
        setTableStateMap(map);
    });

// Table Component-------------------------------
// ... your other imports and code

export const Table: React.FC<TableProps> = ({
    id,
}) => {
    let tableState: TableState | undefined;
    if (id) {
        tableState = stateMap[id]; // 现在这将正确地使用动态 id 访问值
    } else {
        tableState = undefined;
    }
// ... rest of your component code
};