js sum of array
[1, 2, 3, 4].reduce((a, b) => a + b, 0)
// Output: 10js sum of array
[1, 2, 3, 4].reduce((a, b) => a + b, 0)
// Output: 10javascript reduce sum
let nums = [1, 2, 3];
nums.reduce((curr, next) => curr + next);reducer in react example
const initialState = {count: 0};
function reducer(state, action) {
switch (action.type) {
case 'increment':
return {count: state.count + 1};
case 'decrement':
return {count: state.count - 1};
default:
throw new Error();
}
}
function Counter() {
const [state, dispatch] = useReducer(reducer, initialState);
return (
<>
Count: {state.count}
<button onClick={() => dispatch({type: 'decrement'})}>-</button>
<button onClick={() => dispatch({type: 'increment'})}>+</button>
</>
);
}reduce method
The reduce() method executes a reducer function (that you provide) on each element of the array, resulting in single output value.
The reducer function takes four arguments:
Accumulator (acc)
Current Value (cur)
Current Index (idx)
Source Array (src)
//syntax
arr.reduce(callback( accumulator, currentValue, [, index[, array]] )[, initialValue])
//example flatten an array
let flattened = [[0, 1], [2, 3], [4, 5]].reduce(
( accumulator, currentValue ) => accumulator.concat(currentValue),
[]
)reducer react
const getTotalItems = (items: CartItemType[]) =>
items.reduce((ack: number, item) => ack + item.amount, 0);Copyright © 2021 Codeinu
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