从localStorage中读取key为'hostarray'的数组,判读数组中是否存在主机地址1.1.1.1，如果不存在则将其插入数组开头在将其存入localStorage

indexOf

function fun(key) {
  let arr = JSON.parse(localStorage.getItem(key)) || [];
  if (!arr || arr.length === 0) {
    localStorage.setItem(key, JSON.stringify(["1.1.1.1"]));
    return;
  }
  if (arr.indexOf("1.1.1.1") === -1) {
    arr.unshift("1.1.1.1");
    localStorage.setItem(key, JSON.stringify(arr));
  }
}

includes

function fun(key) {
  let arr = JSON.parse(localStorage.getItem(key)) || [];
  if (!arr || arr.length === 0) {
    localStorage.setItem(key, JSON.stringify(["1.1.1.1"]));
    return;
  }
  if (!arr.includes("1.1.1.1")) {
    arr.unshift("1.1.1.1");
    localStorage.setItem(key, JSON.stringify(arr));
  }
}

find

function fun(key) {
  let arr = JSON.parse(localStorage.getItem(key)) || [];
  if (!arr || arr.length === 0) {
    localStorage.setItem(key, JSON.stringify(["1.1.1.1"]));
    return;
  }
  const isv = arr.find((elem) => elem === "1.1.1.1");
  if (!isv) {
    arr.unshift("1.1.1.1");
    localStorage.setItem(key, JSON.stringify(arr));
  }
}

• some

function fun(key) {
  let arr = JSON.parse(localStorage.getItem(key)) || [];
  if (!arr || arr.length === 0) {
    localStorage.setItem(key, JSON.stringify(["1.1.1.1"]));
    return;
  }
  const isv = arr.some((elem) => elem === "1.1.1.1");
  if (!isv) {
    arr.unshift("1.1.1.1");
    localStorage.setItem(key, JSON.stringify(arr));
  }
}

调用

fun("hostarray");