JS手动实现解析JSON

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测试

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console.log(parseText(`
{
  "transformRequest":
  {},
  "transformResponse":
  {},
  "timeout": 10000,
  "xsrfCookieName": "XSRF-TOKEN",
  "xsrfHeaderName": ["X-XSRF-TOKEN","X-XSRF-TOKEN2","X-XSRF-TOKEN3"],
  "maxContentLength": -1,
  "headers":
  {
      "Accept": "application/json, text/plain, */*",
      "Content-Type": "application/json;charset=UTF-8"
  },
  "baseURL": "/test",
  "method": "post",
  "url": "/test",
  "data": "{\\"page\\":1,\\"limit\\":10}"
}`));

实现

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let tokenReg = {
  string: new RegExp("^(\"([^\"\\\\]|\\\\.)*\")"),
  number: new RegExp("^(-?\\d+(\\.\\d+)?)"),
  boolean: new RegExp("^(true|false)"),
  null: new RegExp("^(null)"),
  objectOpen: new RegExp("^(\\{)"),
  objectClose: new RegExp("^(\\})"),
  arrayOpen: new RegExp("^(\\[)"),
  arrayClose: new RegExp("^(\\])"),
  colon: new RegExp("^(\\:)"),
  split: new RegExp("^(\\,)"),
  space: new RegExp("^(\\s+)"),
}

function getFirstToken(text, type) {
  if (!tokenReg[type].test(text)) {
    return null;
  }
  return {
    type,
    match: text.match(tokenReg[type])[1]
  };
}

function transString(text) {
  let val = "";
  for (let i = 1; i < text.length - 1; i++) {
    if (text[i] != "\\") {
      val += text[i];
    } else {
      switch (text[i + 1]) {
        case "n":
          val += "\n";
          break;
        case "t":
          val += "\t";
          break;
        default:
          val += text[i + 1];
          break;
      }
      i++;
    }
  }
  return val;
}

function parseTokens(tokens, index) {
  switch (tokens[index].type) {
    case "objectOpen": {
      index++;
      let obj = {};
      while (tokens[index].type != "objectClose") {
        if (tokens[index].type == "string" && tokens[index + 1].type == "colon") {
          let item = parseTokens(tokens, index + 2);
          obj[transString(tokens[index].match)] = item.data;
          index = item.nextIndex;
          if (tokens[index].type == 'split') {
            index++;
          }
        } else {
          throw new Error();
        }
      }
      return {
        nextIndex: index + 1,
        data: obj
      };
    }
    case "arrayOpen": {
      index++;
      let obj = [];
      while (tokens[index].type != "arrayClose") {
        let item = parseTokens(tokens, index);
        obj.push(item.data);
        index = item.nextIndex;
        if (tokens[index].type == 'split') {
          index++;
        }
      }
      return {
        nextIndex: index + 1,
        data: obj
      };

    }
    case "string": {
      return {
        nextIndex: index + 1,
        data: transString(tokens[index].match)
      };
    }
    case "number": {
      return {
        nextIndex: index + 1,
        data: Number(tokens[index].match)
      };
    }
    case "boolean": {
      return {
        nextIndex: index + 1,
        data: Boolean(tokens[index].match)
      };
    }
    case "null": {
      return {
        nextIndex: index + 1,
        data: null
      };
    }
    default:
      throw new Error();
  }
}

function formatTokens(tokens) {
  let format = "";
  let deepth = 0;
  const enter = (dp) => format += "\n" + "  ".repeat(dp);
  for (let item of tokens) {
    if (item.type == 'objectClose' || item.type == 'arrayClose') {
      enter(--deepth);
    }
    format += item.match;
    if (item.type == 'objectOpen' || item.type == 'arrayOpen') {
      enter(++deepth);
    }
    if (item.type == 'split') {
      enter(deepth);
    }
    if (item.type == 'value') {
      format += " ";
    }
  }
  return format;
}

function parseText(text) {
  let tokens = [];
  while (text) {
    let item
    for (let k in tokenReg) {
      item = getFirstToken(text, k);
      if (item) {
        break;
      }
    }
    tokens.push(item);
    text = text.substring(item.match.length);
  }
  tokens = tokens.filter(o => o.type != "space");
  console.log(formatTokens(tokens));
  return parseTokens(tokens, 0).data;
}
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