How to correctly write this in Typescript?
var obj = {
kv: {
foo: 'bar',
bar: 'baz'
}
};
for(const k in obj.kv) {
const v = obj.kv[k];
obj.kv[k] = 'prefix' + v;
// error TS7017: Index signature of object type implicitly has an 'any' type.
}
// desired output:
// { kv: { foo: 'prefixbar', bar: 'prefixbaz' } }
I want to update each item on the obj.kv object.
You can refactor it this way:
var obj = {
kv: {
foo: 'bar',
bar: 'baz'
}
};
for (const k of Object.keys(obj.kv))
{
const v = (obj.kv as any)[k];
(obj.kv as any)[k] = 'prefix' + v;
}
const obj = {
kv: {
foo: 'bar',
bar: 'baz'
}
};
Object.entries(obj.kv).forEach(([key, value]) => {
obj.kv[key] = `prefix${value}`;
});
Note that the entries method was added in ECMAScript 2016. If you do not have it available, natively or via a polyfill, you can write
Object.entries(obj.kv)
.map(key => [key, obj.kv[key]])
.forEach(([key, value]) => {
obj.kv[key] = `prefix${value}`;
});
instead.
Object.entries but preserves the fluent characteristics and destructuring. Thanks again for your comment.While a bit verbose, this would be more type-friendly:
var obj = {
kv: {
foo: 'bar',
bar: 'baz'
} as {
[key:string]: string,
}
};
for (const k of Object.keys(obj.kv)) {
const v = obj.kv[k];
// error TS2345: Argument of type 'string' is not assignable to parameter of type 'number'.
// const erroneous = Math.round(v);
obj.kv[k] = 'prefix' + v;
}
as { [key:string]: string }, you could write for (const k of Object.keys(obj.kv).map(k => k as keyof typeof obj.kv)) { const v = obj.kv[k]; }. That way, you don't lose strong typing on subsequent property accesses to obj.kv