Why doesn't ts call the function when declaring a variable, indicating a type error-CodePudding

link
refrence:

const fn1 = (arg1: {
    key: number,
})=>{
    console.log(arg1)
}

fn1({
 key: 1
})

const data = {
    key: 1,
    a: 1,
}
fn1(data)

fn1({
    key: 1,
    a: 1,
})

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who can give some help: Why doesn't ts call the function when declaring a variable, indicating a type error

CodePudding user response：

const fn1 = (arg1: {
    key: number,
})=>{
    console.log(arg1)
}

here you declare that the parameter should have a key named "key" and a value as a number, nothing more. if you want to create a type for a parameter that should expect any any key with a number value pair, you need to change it as

const fn1 = (arg1: {
    [k: string]: number
})=>{
    console.log(arg1)
}

CodePudding user response：

To solve the error

As the error message suggest:

Object literal may only specify known properties, and 'a' does not exist in type '{ key: number; }'

It is the difference between object literal and a named object.

However, you can still make your function generic to make it compiles.

const fn1 = <T extends {key: number}>(arg1: T)=>{
    console.log(arg1)
}

Edit

Maybe your question is why, but not how. It is acutally a feature introduced in TypeScript 1.6 to catch programmer human errors on misspelling the property names.

You can turn on suppressImplicitAnyIndexErrors in your tsconfig if you prefer to ignore it. But it is generally not recommended by typescript.