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January 15, 2019 22:16
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a (very naive) json parser in javascript
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| function parse_json(jsonStr) { | |
| let tokens = []; | |
| for (let i = 0; i < jsonStr.length; i++) { | |
| if (jsonStr[i] === '"') { | |
| value = ''; | |
| i++ ; | |
| while (jsonStr[i] !== '"') { | |
| value += jsonStr[i]; | |
| i++; | |
| if (jsonStr[i] === "\\" && jsonStr[i + 1] === "\"") { | |
| value += "\""; | |
| i += 2 | |
| } | |
| } | |
| tokens.push({ | |
| type: 'string', | |
| value | |
| }) | |
| } | |
| //number regex is more like "(?:NaN|-?(?:(?:\\d+|\\d*\\.\\d+)(?:[E|e][+|-]?\\d+)?|Infinity))"; | |
| if (/[0-9]+/.test(jsonStr[i])) { | |
| let value = ''; | |
| while (/[0-9]/.test(jsonStr[i])) { | |
| value += jsonStr[i]; | |
| i++; | |
| } | |
| tokens.push({ | |
| type: "number", | |
| value: parseFloat(value) | |
| }); | |
| } | |
| if (jsonStr.slice(i, i + 4) === "null") { | |
| tokens.push({ | |
| type: 'null', | |
| value: null | |
| }) | |
| } | |
| if (/^true|false$/.test(jsonStr.slice(i,i+5))) { | |
| tokens.push({ | |
| type: 'boolean', | |
| value: (jsonStr.slice(i,i+4) === "true") | |
| }) | |
| } | |
| if (jsonStr[i] === "{") { | |
| tokens.push({ | |
| type: 'curly_open', | |
| value: "{" | |
| }) | |
| } | |
| if (jsonStr[i] === "}") { | |
| tokens.push({ | |
| type: 'curly_close', | |
| value: "}" | |
| }) | |
| } | |
| if (jsonStr[i] === ",") { | |
| tokens.push({ | |
| type: 'comma', | |
| value: "," | |
| }) | |
| } | |
| if (jsonStr[i] === "[") { | |
| tokens.push({ | |
| type: 'bracket_open', | |
| value: "[" | |
| }) | |
| } | |
| if (jsonStr[i] === "]") { | |
| tokens.push({ | |
| type: 'bracket_close', | |
| value: "]" | |
| }) | |
| } | |
| if (jsonStr[i] === ":") { | |
| tokens.push({ | |
| type: 'colon', | |
| value: ":" | |
| }) | |
| } | |
| } | |
| return tokens; | |
| } | |
| function parser(tokens, obj = {}) { | |
| if (!tokens.length) return obj; | |
| const current = tokens.shift(); | |
| switch (current.type) { | |
| case "curly_open": | |
| if (Array.isArray(obj)) obj.push(parser(tokens)) | |
| break; | |
| case "bracket_close": | |
| case "curly_close": | |
| return obj | |
| case "boolean": | |
| return current.value; | |
| case "string": | |
| if (tokens[0].type === "colon"){ | |
| const key = current.value; | |
| tokens.shift(); | |
| obj[key] = parser(tokens); | |
| return parser(tokens, obj) | |
| } | |
| case "number": | |
| case "null": | |
| if (Array.isArray(obj)) obj.push(current.value); | |
| else return current.value; | |
| break; | |
| case "bracket_open": | |
| return parser(tokens, []); | |
| } | |
| return parser(tokens, obj) | |
| } | |
| let OBJ = { | |
| a: { | |
| bb: "str", | |
| b: { | |
| sea: [{ | |
| x: { 7: 90 } | |
| }, 2, 3, 4, 5], | |
| d: {2:null,4:[1,2,3,{a:true}]}, | |
| e: null, | |
| f: "some crazy \" \" gnarly string" | |
| } | |
| }, | |
| g: 1, | |
| x: false, | |
| y: true | |
| } | |
| let myTokens = parse_json(JSON.stringify(OBJ)); | |
| let parsedObj = parser(myTokens) | |
| console.log(JSON.stringify(parsedObj, null, 4)); | |
| const assert = require('assert'); | |
| assert.deepEqual(parsedObj,OBJ) |
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