forEach终止循环

面试主题：【循环】【forEach】【JS】

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问：forEach如何退出循环

答：无法常规退出循环，需要使用

       try { throw new Error(msg) } catch (error) {}捕获异常终止

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测试思路：

常规循环

捕获异常退出循环

常规退出循环：return

常规退出循环：break

/**
 * forEach如何终止循环
 */
let demo = (window.demo = {}),
  ary = [2, 4, 6, 8],
  newAry = [];
demo.Constants = {
  LAST_ITEM_INDEX: 1, //用于获取数组最后一个元素
  EQUEAL_CONDITION: "满足条件,跳出循环" //异常信息
};

demo.commonForEach = (ary, newAry) => {
  if (!(ary instanceof Array)) return;
  ary.forEach(function(item) {
    newAry.push(item);
  });
  console.log("循环结束,newAry:", newAry);
};
demo.commonForEach(ary, newAry);

 常规循环结果：

　　

/**
 * forEach如何终止循环
 */
let demo = (window.demo = {}),
  ary = [2, 4, 6, 8],
  newAry = [];
demo.Constants = {
  LAST_ITEM_INDEX: 1, //用于获取数组最后一个元素
  EQUEAL_CONDITION: "满足条件,跳出循环" //异常信息
};
demo.tryCatchForEach = (ary, newAry, breakItem) => {
  if (!(ary instanceof Array)) return;
  if (Boolean(newAry.length)) {
    newAry = [];
  }
  let breakItemValue = breakItem || ary.length - demo.Constants.LAST_ITEM_INDEX;
  try {
    ary.forEach(function(item) {
      if (item == breakItemValue) {
        throw new Error(demo.Constants.EQUEAL_CONDITION);
      }
      newAry.push(item);
    });
    console.log("循环结束,newAry:", newAry);
  } catch (error) {
    if (!Boolean(newAry.length)) {
      console.log(error.message);
    } else {
      console.log("循环被终止,newAry:", newAry);
    }
  }
};
demo.tryCatchForEach(ary, newAry, ary[1]);
demo.tryCatchForEach(ary, newAry, ary[0]);

捕获异常退出循环结果：

　　

/**
 * forEach如何终止循环
 */
let demo = (window.demo = {}),
  ary = [2, 4, 6, 8],
  newAry = [];
demo.Constants = {
  LAST_ITEM_INDEX: 1, //用于获取数组最后一个元素
  EQUEAL_CONDITION: "满足条件,跳出循环" //异常信息
};
demo.returnForEach = (ary, newAry, breakItem) => {
  if (!(ary instanceof Array)) return;
  if (Boolean(newAry.length)) {
    newAry = [];
  }
  let breakItemValue = breakItem || ary.length - demo.Constants.LAST_ITEM_INDEX;
  ary.forEach(function(item) {
    if (item == breakItemValue) {
      return;
    }
    newAry.push(item);
  });
  console.log("循环结束,newAry:", newAry);
};
demo.returnForEach(ary, newAry, ary[1]);

常规退出循环-return结果：

　　

/**
 * forEach如何终止循环
 */
let demo = (window.demo = {}),
  ary = [2, 4, 6, 8],
  newAry = [];
demo.Constants = {
  LAST_ITEM_INDEX: 1, //用于获取数组最后一个元素
  EQUEAL_CONDITION: "满足条件,跳出循环" //异常信息
};
demo.berakForEach = (ary, newAry, breakItem) => {
  if (!(ary instanceof Array)) return;
  if (Boolean(newAry.length)) {
    newAry = [];
  }
  let breakItemValue = breakItem || ary.length - demo.Constants.LAST_ITEM_INDEX;
  ary.forEach(function(item) {
    if (item == breakItemValue) {
      break;
    }
    newAry.push(item);
  });
  console.log("循环结束,newAry:", newAry);
};
demo.berakForEach(ary, newAry, ary[1]);

常规退出循环-break：