检查对象是否符合打字稿中的定义

Question

I've a data structure like this

"properties": {
    "email": {
        "type": "string",
        "validations": ["required", "email"]
    },
    "address": {
        "street": {
            "type": "string",
            "validations": ["required"]
        },
        "zip": {
            "type": "number",
            "validations": ["required", "min(5)", "max(5)"]
        }
    }
}

Then I iterate on it using Object.entries(...) How can I check if the object is either of the first type or the second one (which is composite)?

I could check for property names, but i want some neat solution using typescript ... any ideas?

Answer 1

Runtime checking is not something that Typescript can help you with, Typescript types are pretty much gone at runtime. What Typescript can help you with is compile time checking. A custom type guard would be helpful to help you check and then have the variable typed correctly:

type Validation = { type: string, validations: string[] }
type ValidationContainer = { [name: string] : Validation | ValidationContainer };

// Type guard
function isValidation (v: Validation | ValidationContainer) : v is Validation {
    let vv = v as Validation;
    return  typeof vv.type === "string" && vv.validations instanceof Array;
}

function processTree(v:ValidationContainer, parent?:string) {
    for(let [key, value] of Object.entries(v)) {
        // value is  Validation | ValidationContainer
        if(isValidation(value)) {
            // value is Validation here after type guard
            console.log(value.type)
            console.log(value.validations)
        }else{
            // value is Validation here after type guard
            processTree(value, key)
        }
    }
}