JavaScript algorithm question: trying to implement a JSON parsing function to output a string in a prettier format

Question

I am well aware of the existence of JSON.parse and JSON.stringify and prettier the npm package. But for some reason I still have to do this by hand. Think of it as a coding interview question and please do not close this question simply because I could have used JSON.parse and JSON.stringify, as I said there is this constraint. And this question is NOT a duplicate of this pretty-print JSON using JavaScript

Here is a string "['foo', {bar:['baz',null,1.0,2]}]"

I wanted to implement a function to return a string denoting a json object with proper indentaion.

i.e. the output string should be

Here is my attempt

function printJSON(str) {
    let spaces = [];
    let output = '';

    str.split('').forEach(char => {
        switch(char) {
            case '{':
            case '[':
                spaces.push('    ');
                output += char + '\n' + spaces.join('');
                break;
            case '}':
            case ']':
                spaces.pop();
                output += '\n' + spaces.join('') + char;
                break;
            case ',':
                output += char + '\n' + spaces.join('');
                break;
            default:
                output += char;
                break;
        }
    });

    console.log(output);
    return output
}

However the output format is slightly off as in

[ 
    "foo", 
     { 
        bar:[ // 
            "baz", 
            null, 
            1.0, 
            2 
        ] 
    } 
]

How can I fix this format issue? also is there a more elegant way or alternative way to achieve this?

score 1 · Accepted Answer · answered Jan 04 '21 at 05:15

What about this, since you also need to add a carriage return after the colon:

function printJSON(str) {
    let spaces = [];
    let output = '';

    str.split('').forEach(char => {
        switch (char) {
            case '{':
            case '[':
                spaces.push('    ');
                output += char + '\n' + spaces.join('');
                break;
            case ':':
                output += char + '\n' + spaces.join('');
                break;
            case '}':
            case ']':
                spaces.pop();
                output += '\n' + spaces.join('') + char;
                break;
            case ',':
                output += char + '\n' + spaces.join('');
                break;
            default:
                output += char;
                break;
        }
    });

    console.log(output);
    return output
}

let string = "['foo', {bar:['baz',null,1.0,2]}]";
printJSON(string);

JavaScript algorithm question: trying to implement a JSON parsing function to output a string in a prettier format

1 Answers1