I have a Json Response
"carts": {
"value": [
{
"Amt": 40
},
{
"Amt": 20.25
},
{
"Amt": 10.30
}
]
}
I want to get the sum value of Amt field and the output should be 70.55 How to get this using Typescript.I am new to typescript. Can anyone please help me with this?
The correct way of using JavaScript's reduce function (which is also valid for TypeScript) would be:
const response = {
"carts": {
"value": [
{
"Amt": 40
},
{
"Amt": 20.25
},
{
"Amt": 10.30
}
]
}
};
const total = response.carts.value.reduce((sum, item) => sum + item.Amt, 0);
console.log(total);Note that if you want to support IE8 you have to include a polyfill (like that on MDN's page).
I am very much in favor of the Rxjs' Observable answer, but since no one else mentioned it : Javascript arrays have a reduce function, so one can use it in Typescript too !
// suppose variable carts already stores the deserialized json
let total: number = carts.value.reduce(
(a: number, b) => a + b.Amt, 0);
after @Stefan's comments :
Fixed mistakes & better to not assign type of b, so that it will be inferred from the context and maybe raise a Typescript error at compile-time.
value and thus your b and your initial value (your first a) are objects.
a and b and let TypeScript infer the types. Otherwise for example if the objects in value don't contain any Amt values using any as type hides the resulting error.any was the actual "default" if nothing was indicated (and no type guards or like are used). (without the noImplicitAny option, which is the default)let x = 0;). If a function definition contains the definition of the callback parameters, those are also automatically inferred (for example the relevant definition for reduce is reduce<U>(callbackfn: (previousValue: U, currentValue: T, currentIndex: number, array: T[]) => U, initialValue: U): U;). typescriptlang.org/docs/handbook/type-inference.html contains useful information about that.You can use observable reduce. If you have Http response then:
this.http.get('url')
.map(response.carts.value)
.map(res => res.Amt)
.reduce((a, b) => a + b)
.subscribe(res => console.log(res))
let sum = 0;
for (var i = 0; i < this.carts.value.length; i++) {
sum+= this.carts.value[i].Amt;
}
You can write a function like this:
public cartTotal(): number {
let total: number = 0;
this.carts.value.forEach((e:any) => {
total = total + Number(e.Amt);
});
return total;
}
e will be an object. Additionally if you want e to be a number it would be better to type annotate it as a number, not any. That way there would be at least a compiler error (which is one aspect why you use TypeScript) if you supply it with an object.This is the basic way to do it.
sum=0;
for(let a of json.carts.value){
sum=sum+a.Amt;
}
