前端操作方法

数组

示例：

1. push():

function push(arr, ...elements) {
  for (let i = 0; i < elements.length; i++) {
    arr[arr.length] = elements[i];
  }
  return arr.length;
}

2. pop():

function pop(arr) {
  if (arr.length === 0) {
    return undefined;
  }
  const lastElement = arr[arr.length - 1];
  arr.length--;
  return lastElement;
}

3. unshift():

function unshift(arr, ...elements) {
  for (let i = arr.length - 1; i >= 0; i--) {
    arr[i + elements.length] = arr[i];
  }
  for (let i = 0; i < elements.length; i++) {
    arr[i] = elements[i];
  }
  return arr.length;
}

4. shift():

function shift(arr) {
  if (arr.length === 0) {
    return undefined;
  }
  const firstElement = arr[0];
  for (let i = 1; i < arr.length; i++) {
    arr[i - 1] = arr[i];
  }
  arr.length--;
  return firstElement;
}

对象

示例：

1. Object.keys():

function keys(obj) {
  const result = [];
  for (let key in obj) {
    if (obj.hasOwnProperty(key)) {
      result.push(key);
    }
  }
  return result;
}

2. Object.values():

function values(obj) {
  const result = [];
  for (let key in obj) {
    if (obj.hasOwnProperty(key)) {
      result.push(obj[key]);
    }
  }
  return result;
}

3. Object.entries():

function entries(obj) {
  const result = [];
  for (let key in obj) {
    if (obj.hasOwnProperty(key)) {
      result.push([key, obj[key]]);
    }
  }
  return result;
}

4. Object.assign():

function assign(target, ...sources) {
  for (let i = 0; i < sources.length; i++) {
    const source = sources[i];
    for (let key in source) {
      if (source.hasOwnProperty(key)) {
        target[key] = source[key];
      }
    }
  }
  return target;
}

字符串

示例：

1. length:

function getLength(str) {
  let count = 0;
  for (let i = 0; i < str.length; i++) {
    count++;
  }
  return count;
}

2. concat():

function concat(str1, str2) {
  return str1 + str2;
}

3. indexOf():

function indexOf(str, searchValue, startIndex = 0) {
  for (let i = startIndex; i < str.length; i++) {
    if (str.slice(i, i + searchValue.length) === searchValue) {
      return i;
    }
  }
  return -1;
}

4. lastIndexOf():

function lastIndexOf(str, searchValue, startIndex = str.length - 1) {
  for (let i = startIndex; i >= 0; i--) {
    if (str.slice(i, i + searchValue.length) === searchValue) {
      return i;
    }
  }
  return -1;
}

5. includes():

function includes(str, searchValue) {
  return str.indexOf(searchValue) !== -1;
}

6. slice():

function slice(str, start, end) {
  let result = '';
  const length = str.length;
  if (start < 0) {
    start = Math.max(length + start, 0);
  } else {
    start = Math.min(start, length);
  }
  if (end === undefined) {
    end = length;
  } else if (end < 0) {
    end = Math.max(length + end, 0);
  } else {
    end = Math.min(end, length);
  }
  for (let i = start; i < end; i++) {
    result += str[i];
  }
  return result;
}

7. replace():

function replace(str, searchValue, replaceValue) {
  return str.split(searchValue).join(replaceValue);
}

8. trim():

function trim(str) {
  return str.replace(/^\s+|\s+$/g, '');
}

9. toUpperCase():

function toUpperCase(str) {
  let result = '';
  for (let i = 0; i < str.length; i++) {
    const charCode = str.charCodeAt(i);
    if (charCode >= 97 && charCode <= 122) {
      result += String.fromCharCode(charCode - 32);
    } else {
      result += str[i];
    }
  }
  return result;
}

10. toLowerCase():

function toLowerCase(str) {
  let result = '';
  for (let i = 0; i < str.length; i++) {
    const charCode = str.charCodeAt(i);
    if (charCode >= 65 && charCode <= 90) {
      result += String.fromCharCode(charCode + 32);
    } else {
      result += str[i];
    }
  }
  return result;
}

11. split():

function split(str, separator, limit) {
  const result = [];
  let start = 0;
  let count = 0;
  for (let i = 0; i < str.length; i++) {
    if (separator === '') {
      result.push(str[i]);
      count++;
    } else if (str.slice(i, i + separator.length) === separator) {
      result.push(str.slice(start, i));
      start = i + separator.length;
      count++;
      if (limit && count >= limit) {
        break;
      }
    }
  }
  result.push(str.slice(start));
  return result;
}

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