Convert a JSONifiable value into valid Apex (Salesforce) using apexify() in JavaScript.

apexify.js

var apexify;
(function() {
  apexify = function(value, indent) {
    indent = indent || 0;
    let indentation = 'string' === typeof indent
      ? indent
      : new Array(indent + 1).join(' ');
    let newLine = indentation ? '\n' : '';
    let allSpacing = indentation ? newLine + indentation : '';
    let space = indentation ? ' ' : '';
    let arrow = space + '=>' + space;
    let comma = ',' + newLine;
    return recurseApexify(
      JSON.parse(JSON.stringify(value)),
      indentation,
      newLine,
      allSpacing,
      arrow,
      comma
    );
  };
  
  function recurseApexify(value, indentation, newLine, allSpacing, arrow, comma) {
    var typeName = Object.prototype.toString.call(value).slice(8, -1);
    if (value === null || typeName === 'Number' || typeName === 'Boolean') {
      return JSON.stringify(value);
    }
    if (typeName === 'Array') {
      let hasData = value.length > 0;
      let myNewLine = hasData ? newLine : '';
      return 'new List<Object>{'
        + myNewLine
        + value
          .map(function(x) {
            return recurseApexify(x, indentation, newLine, allSpacing, arrow, comma);
          })
          .join(comma)
          .replace(/^/gm, indentation)
        + myNewLine
        + '}';
    }
    if (typeName === 'String') {
      return "'"
        + value.replace(/'/g, "\\'").replace(/[^\x20-z]/g, substringify)
        + "'";
    }
    let keys = Object.keys(value);
    let hasData = keys.length > 0;
    let myNewLine = hasData ? newLine : '';
    return 'new Map<String,Object>{'
      + myNewLine
      + keys
        .map(function(key) { return recurseApexify(key) + arrow + recurseApexify(value[key], indentation, newLine, allSpacing, arrow, comma); })
        .join(comma)
        .replace(/^/gm, hasData ? indentation : '')
      + myNewLine
      + '}';
  }

  function substringify(x) {
    return JSON.stringify(x).slice(1, -1);
  }
})();

~apexifyInIO.js

function apexifyInIO(value, tabSize) {
  return apexify(JSON.parse(value), tabSize);
}

~example.js

// HIDE \\
console.load('local://apexify.js');

// \\
var data = {"success": false, "error": "Authentication failed.", "u":{value:null}, user:{first:'Chris',last:'West',grades:[1,2,3,4,5],details:'sdf\n\t\rxcvxc'}};

// Normal call without indents
console.log(apexify(data));

// \\
// Call with indenting (number of spaces)
console.log(apexify(data, 3));


// \\
// Call with indenting (specify single spacing)
console.log(apexify(data, '\t'));

~gist-hack.js

function getPageParts(params) {
  return {
    title: "Apexify - Convert JSON To Apex",
    description: "Easily conversion any JSON into Salesforce Apex notation.",
    buttons: { submit: 'Convert', clear: false }
  };
}

function getInputs(params) {
  var inputs = params.inputs;
  
  function onInput(value) {
    try {
      JSON.parse(value);
    }
    catch (e) {
      this.reportError('The specified JSON is invalid.');
    }
  }

  return [
    {
      key: 'json',
      label: 'JSON',
      type: 'code',
      lang: 'json',
      value: inputs.json && inputs.json.value,
      onInit: onInput,
      onInput: onInput
    }
  ];
}

function getOutputs(params) {
  var inputs = params.inputs;
  var apexCode = apexify(params.inputs.json, 2);
  return [
    { 
      label: 'Salesforce Apex',
      type: 'code',
      lang: 'apex',
      value: apexCode
    },
    {
      label: 'Download Apex Code',
      type: 'download-button',
      value: apexCode,
      downloadName: 'example.apex'
    }
  ];
}

eval(GIST_FILES['apexify.js'].text);

~io-config.jsonc

{
  // Title of the IO App
  "title": "apexify()",
  // Name of the function responsable for transforming the input into the output.
  "transform": "apexifyInIO",
  // Where to find the code that will be eval'd.
  "files": ["apexify.js", "~apexifyInIO.js"],
  // Input setup
  "input": { "language": "json" },
  // Output setup
  "output": { "language": "apex" },
  // Parameters that can be set.
  "params": [
    {
      "type": "number",
      "label": "Indentation (Spaces)",
      "name": "tabSize",
      "value": 4
    }
  ],
  // Type of YourJS IO-App
  "type": "instant"
}

~README.md

JavaScript Snippet - apexify()

You can use this simple function to turn JSON into Apex equivalent.

console.load('local://~example.js');

Here is the Gistly page:
https://www.yourjs.com/gistly/d0240a1295d4df88d1e1c53bf911b241/~README.md

Here is the IO App:
https://www.yourjs.com/gist-io/d0240a1295d4df88d1e1c53bf911b241