I am using this code to iterate through a custom object:

interface TableItemBody {
    [fieldId: string]: string
}

interface TableItem {
    [tabId: string]: TableItemBody | TableItemBody[]
}

const iterate = (entry: TableItem) => {
    for (const tabId of Object.keys(entry)) {
        if (Array.isArray(entry[tabId])) {
            for (const idx of entry[tabId]) {
                for (const fieldId of Object.keys(entry[tabId][idx])) {
                    console.log(fieldId)
                }
            }
        } else {
            for (const fieldId of Object.keys(entry[tabId])) {
                console.log(fieldId)
            }
        }
    }
}

const tableItem: TableItem = {
    tab1: {
        field1: 'fieldValue'
    },
    tab2: [{
        field2: 'fieldValue'
    }]
}

iterate(tableItem)

However, I am getting two errors. The first one is Type 'TableItemBody | TableItemBody[]' must have a '[Symbol.iterator]()' method that returns an iterator. I am using Array.isArray(entry[tabId]) to ensure that I am actually iterating through an array. So why does this error appear?

If you want to play with that code, here is the link the to typescript playground.

CodePudding user response：

You need to cast it to TableItemBody[]. Look here

const iterate = (entry: TableItem) => {
    for (const tabId of Object.keys(entry)) {
        if (Array.isArray(entry[tabId])) {
            const tableItems = entry[tabId] as TableItemBody[]
            for (const tableItem of tableItems) {
                for (const fieldId of Object.keys(tableItem)) {
                    console.log(fieldId)
                }
            }
        } else {
            for (const fieldId of Object.keys(entry[tabId])) {
                console.log(fieldId)
            }
        }
    }
}