Array.prototype.reduce()方法应用实践
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统计一个字符串中每个字母出现的次数？
function showCount(str) {
return str.split('').reduce((sum, item) => {
sum[item] ? ++sum[item] : sum[item] = 1
return sum;
}, {});
}
let str = 'sdfasdfeewe';
showCount(str)
//{"s": 2,"d": 2,"f": 2,"a": 1,"e": 3,"w": 1}
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给定一对象和一数组，从该对象中依据该数组给定的key值筛选出一个新对象？
function extractObj(obj) {
if(Object.prototype.toString.call(obj) !== '[object Object]') {
throw new Error("The param is JSON's Object type");
}
return function(extractKeys) {
if(Object.prototype.toString.call(extractKeys) !== '[object Array]') {
throw new Error('The param is Array type');
}
return extractKeys.reduce((extractObj, key) => {
if(!obj[key]) return extractObj;
extractObj[key] = obj[key];
return extractObj;
}, {});
}
}
let a = {name: 'sgg', age: 24, phone: 1234567789};
let extractA = extractObj(a);
extractA(['name', 'hello', 'age'])
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使用reduce方法，实现对一个对象中的多个属性分别执行多次叠加（修改）操作？ —— 处理Obj
// state加工的工厂(工人+工料 = 产品)
function combineReducer(reducers) {
return function(state, actions) {
actions.forEach((action) => {
Object.keys(reducers).reduce((state, keys) => {
reducers[keys](state, action);
return state;
}, state)
});
return state;
}
}
// 创建一个产品， state
let state = {
iphone: 10000,
iwatch: 500
}
// state加工的工人
let reducers = {
dealIPhonePrice(state, action) {
state.iphone += action.price;
return state;
},
dealIWatchPrice(state, action) {
state.iwatch *= action.range;
return state;
}
};
// state加工的工料
let actions = [
{price: 100, range: 1.1},
{price: 180, range: 1.08},
{price: 280, range: 1.2}
]
//雇佣工人进厂，准备干活
let rootReducer = combineReducer(reducers);
//工人(reducers)把工料(actions) 加工成产品(state)
rootReducer(state, actions)
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利用reduce实现一个组合函数？ —— 处理Function
//组合多个函数，reduce版
function composeFn(...funcs) {
return funcs.reduce((a,b) => args => a(b(args)));
}
//for循环版(功能，同上)
function composeFn(...funcs) {
return function(args) {
let len = funcs.length - 1;
for(let i=len; i>=0; i-=2) {
args = i > 0 ? funcs[i-1](funcs[i](args))
: funcs[i](args);
}
return args;
}
}
// ****** demo ******
function fn1(arg) {
return arg * 2;
}
function fn2(arg) {
return arg + 10;
}
let composeAfterFn = composeFn(fn1, fn2);
composeAfterFn(1);
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描述如下代码的执行过程及结果
let arr = [];
for(let i=0; i<10; i++) {
arr.push((foo) => {
console.log(i);
return function() {
foo();
}
});
}
let boo = arr.reduce((pre, cur) => {
return cur(pre);
});
// => 1 2 3 4 5 6 7 8 9
boo()
// => 0