# 实现下面代码
function repeat(s, count) {}
repeat("s", 3); // 输出 ‘sss’
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- 实现下面代码
// 正则匹配标签名 输出div p span
<div>
<p>
<span></span>
</p>
<span></span>
</div>
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- 请实现 find 函数，使下列的代码调用正确。
// 约定：
// title数据类型为String
// userId为主键，数据类型为Number
var data = [
{ userId: 8, title: "title1" },
{ userId: 11, title: "other" },
{ userId: 15, title: null },
{ userId: 19, title: "title2" },
];
var find = function(origin) {
// your code are here...
};
// 查找 data 中，符合条件的数据，并进行排序
var result = find(data)
.where({
title: /\d$/,
})
.orderBy("userId", "desc");
console.log(result); // [{ userId: 19, title: 'title2'}, { userId: 8, title: 'title1' }];
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- 实现 sendRequest(promises, max, callback)，同时最多执行 max 个 promises，超过的等待有空闲的开始执行，执行完成后执行 callback
function sendRequest(promises, max, callback) {
let current = 0;
const results = [];
const originLen = promises.length;
const next = () => {
while (current < max && promises.length) {
const index = originLen - promises.length;
const promise = promises.shift();
results[index] = {
value: null,
reason: null,
};
Promise.resolve(promise)
.then(
(value) => {
results[index].value = value;
},
(reason) => {
results[index].reason = reason;
}
)
.finally(() => {
current--;
next();
});
current++;
}
if (current === 0) {
callback(results);
}
};
next();
}
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- 实现 findFirstIndex 函数，找到有序数组 [1, 2, 3, 4, 7, 7, 7, 9, 12, 23, 34, 45, 55, 67]中第一次出现的位置，比如 7 第一次出现的位置是 4
function findFirstIndex(arr, target) {
let begin = 0;
let end = arr.length;
while (begin < end) {
const mid = (begin + end) >>> 1;
if (arr[mid] >= target) {
end = mid;
} else {
begin = mid + 1;
}
}
if (begin === arr.length) return -1;
return arr[begin] === target ? begin : -1;
}
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- 十进制转换成任意进制
function tenToOther(num, base) {
const baseNumber = "0123456789abcdefghijklmnopqrstuvwxyz";
const result = [];
while (num) {
const rest = num % base;
num = Math.floor(num / base);
result.unshift(baseNumber[rest]);
}
return result.join("");
}
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- 大数相加
function bigAdd(a, b) {
const aArr = a.split("");
const bArr = b.split("");
let flag = 0;
let result = [];
while (aArr.length || bArr.length) {
const left = aArr.pop() || 0;
const right = bArr.pop() || 0;
const value = Number(left) + Number(right) + flag;
result.unshift(value % 10);
flag = parseInt(value / 10);
}
if (flag) {
result.unshift(flag);
}
return result.join("");
}
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- 深拷贝
function deepClone(obj, map = new WeakMap()) {
if (obj === null || typeof obj !== "object") {
return obj;
}
if (map.has(obj)) {
return map.get(obj);
}
const copy = Array.isArray(obj) ? [] : {};
map.set(obj, copy);
const keys = Reflect.ownKeys(obj);
keys.forEach((key) => {
copy[key] = deepClone(obj[key], map);
});
return copy;
}
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- 图片懒加载写代码
function lazyload() {
const observe = new IntersectionObserver((enteris) => {
enteris.forEach((entry) => {
const lazyImage = entry.target;
if (
entry.isIntersecting &&
lazyImage.getAttribute("src") == "loading.gif"
) {
lazyImage.src = lazyImage.dataset.src;
observe.unobserve(lazyImage);
}
});
});
for (let i = 0; i < imgs.length; i++) {
observe.observer(imgs[i]);
}
}
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