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Serialization of JS object with different logic for object's properties

Hi I need to convert the the numeric values of my object to string. But different properties has different transformation rules.
My sample object:
{
name: "Name"
sRatio: 1.45040404
otherMetric: 0.009993
}
I use JSON.stringify to convert my initial object.
let replacemet = {}
JSON.stringify(metrics[0], function (key, value) {
//Iterate over keys
for (let k in value) {
if ((k !== "sRatio") || (k !== "name")) {
replacemet[k] = (100*value[k]).toFixed(2) + "%"
} else {
if( k === "name") {
replacemet[k] = "yo!"+value[k]
} else{
replacemet[k] = value[k].toFixed(2)
}
}
}
})
But my conditions are not triggered and all properties are converting on the same manner.

The job of the replacer callback is not to fill in some global replacemet object but rather to return a new value.
I think you are looking for something along the lines of
JSON.stringify(sample, function (key, value) {
if (key == "sRatio") {
return value.toFixed(2);
} else if (key == "name") {
return "yo!"+value;
} else if (typeof value == "number") {
return (100*value).toFixed(2) + "%"
} else {
return value;
}
})

Try using switch block that will be really good for this. Detailed description on switch.
let replacemet = {}
JSON.stringify(metrics[0], function (key, value) {
//Iterate over keys
for (let k in value) {
switch(k) {
case "name":
replacemet[k] = "yo!"+value[k];
break;
case "sRatio":
replacemet[k] = value[k].toFixed(2);
break;
default:
replacemet[k] = value[k].toFixed(2);
}
}
})

Hope to help you . I add when dynamic property
metrics =
[
{
name: "Name",
sRatio: 1.45040404,
otherMetric:0.009993
},
{
name: "Name1",
sRatio: 2.45040404,
otherMetric: 1.009993
}
]
;
let source = JSON.stringify(metrics);
let arrJson = new Array();
//arrJson = {};
metrics.forEach(function(value){
let replacemet = {};
for(var k in value) {
if( k.toString().trim() == "name") {
replacemet[k] = "yo!"+value[k] ;
}
else
if ( ( k.toString().trim() !== "sRatio") && ( k.toString().trim() !== "name")) {
replacemet[k] = (100* value[k] ).toFixed(2).toString() + "%" ;
} else {
replacemet[k] = value[k].toFixed(2) ;
}
}
arrJson.push(JSON.stringify(replacemet)) ;
});
console.log(arrJson);

How to implement lambda /anonymous functions in JavaScript

So I am trying to implement a subset of LISP using JavaScript. I am stuck on two things related to lambdas.
How to implement the ability to create a lambda and at the same time feed it the arguments and have it immediately evaluated? For example:
((lambda(x)(* x 2)) 3)
For now I hard-coded this functionality in my eval-loop like this:
else if (isArray(expr)){
if (expr[0][0] === 'lambda' || expr[0][0] === 'string') {
console.log("This is a special lambda");
var lambdaFunc = evaluate(expr[0], env)
var lambdaArgs = [];
for(var i = 1; i < expr.length; i++){
lambdaArgs.push(expr[i]);
}
return lambdaFunc.apply(this, lambdaArgs);
}
Now this works, and if I write the above lambda with the parameter it will evaluate to 6, however, I am wondering if there is any smarter way to implement this?
If a lambda is instead bound to a symbol, for example:
(define fib (lambda(n)
(if (< n 2) 1
(+ (fib (- n 1))(fib (- n 2)))
)))
In this case, the (define fib) part will be evaluated by the eval-loop first, just as if fib was simply being assigned a number:
else if (expr[0] === 'define') { // (define var value)
console.log(expr + " is a define statement");
var newVar = expr[1];
var newVal = evaluate(expr[2], env);
env.add(newVar, newVal);
return env;
}
And the lambda-function is being created like this:
else if (expr[0] === 'lambda') { // (lambda args body)
console.log(expr + " is a lambda statement");
var args = expr[1];
var body = expr[2];
return createLambda(args, body, env);
}
Separate function to create the lambda:
function createLambda(args, body, env){ // lambda args body
function runLambda(){
var lambdaEnvironment = new environment(env, "lambda environment");
for (var i = 0; i < arguments.length; i++){
lambdaEnvironment.add(args[i], evaluate(arguments[i], env));
}
return evaluate(body, lambdaEnvironment);
}
return runLambda;
}
This works fine for lambdas such as:
(define range (lambda (a b)
(if (= a b) (quote ())
(cons a (range (+ a 1) b)))))
(define fact (lambda (n)
(if (<= n 1) 1
(* n (fact (- n 1))))))
For example, (range 0 10) returns a list from 0 to 10.
But if I try a lambda within a lambda, it does not work. For example:
(define twice (lambda (x) (* 2 x)))
(define repeat (lambda (f) (lambda (x) (f (f x)))))
I would expect the following to return 40:
((repeat twice) 10)
But instead, it returns a list looking like this:
function runLambda(){ var lambdaEnvironment = new environment(env, "lambda
environment"); for (var i = 0; i < arguments.length; i++){
lambdaEnvironment.add(args[i], evaluate(arguments[i], env)); } return
evaluate(body, lambdaEnvironment); },10
Any ideas what might be missing here?
Full JavaScript;
//functions for parsing invoice String
function parse(exp) {
return readFromTokes(tokenize(exp));//code
}
function isNumeric(arg){
return !isNaN(arg);
}
function isArray(obj){
return !!obj && obj.constructor === Array;
}
function readFromTokes(exp){
//Create abstract syntax tree
if (exp.length == 0) {
}
var token = exp.shift();
if (token == '('){
var L = [];
while (exp[0] != ')') {
L.push(readFromTokes(exp));
}
exp.shift(); //remove end paranthesis
return L;
} else {
if (token == ')') {
console.log("Unexpected )");
} else {
return atom(token);
}
}
}
function tokenize(exp){
//Convert a program in form of a string into an array (list)
var re = /\(/g;
var re2 = /\)/g;
exp = exp.replace(re, " ( ");
exp = exp.replace(re2, " ) ");
exp = exp.replace(/\s+/g, ' ');
exp = exp.trim().split(" ");
return exp;
}
function atom(exp){
if (isNumeric(exp)) {
return parseInt(exp); //A number is a number
} else {
return exp; //Everything else is a symbol
}
}
function environment(parentEnvironment, name){
var bindings = [];
var parent = parentEnvironment;
var name = name;
function add(variable, value){
console.log("variable: " + variable + " value: " + value);
bindings.push([variable, value]);
}
function printName(){
console.log(name);
}
function print() {
console.log("printing environment: ")
for (var i = 0; i < bindings.length; i++){
console.log(bindings[i][0] + " " + bindings[i][1]);
}
}
function get(variable){
for (var i = 0; i < bindings.length; i++){
if (variable == bindings[i][0]){
return bindings[i][1];
}
}
if (parent != null){
return parent.get(variable);
} else {
console.log("No such variable");
return false;
}
}
function getParent(){
return parent;
}
this.add = add;
this.get = get;
this.getParent = getParent;
this.print = print;
this.printName = printName;
return this;
}
function addPrimitives(env){
env.add("+", function() {var s = 0; for (var i = 0; i<arguments.length;i++){ s += arguments[i];} return s});
env.add("-", function() {var s = arguments[0]; for (var i = 1; i<arguments.length;i++){ s -= arguments[i];} return s});
env.add("*", function() {var s = 1; for (var i = 0; i<arguments.length;i++){ s *= arguments[i];} return s});
env.add("/", function(x, y) { return x / y });
env.add("false", false);
env.add("true", true);
env.add(">", function(x, y){ return (x > y) });
env.add("<", function(x, y){ return (x < y) });
env.add("=", function(x, y){ return (x === y)});
env.add(">=", function(x, y){ if (x >= y){return true;} else {return false;}});
env.add("<=", function(x, y){ if (x <= y){return true;} else {return false;}});
env.add("eq?", function() {var s = arguments[0]; var t = true; for(var i = 1; i<arguments.length; i++){ if (arguments[i] != s) {t = false }} return t;});
env.add("cons", function(x, y) { var temp = [x]; return temp.concat(y); });
env.add("car", function(x) { return x[0]; });
env.add("cdr", function(x) { return x.slice(1); });
env.add("list", function () { return Array.prototype.slice.call(arguments); });
env.add("list?", function(x) {return isArray(x); });
env.add("null", null);
env.add("null?", function (x) { return (!x || x.length === 0); });
}
function createLambda(args, body, env){ // lambda args body
function runLambda(){
var lambdaEnvironment = new environment(env, "lambda environment");
for (var i = 0; i < arguments.length; i++){
lambdaEnvironment.add(args[i], evaluate(arguments[i], env));
}
return evaluate(body, lambdaEnvironment);
}
return runLambda;
}
function evaluate(expr, env) {
console.log(expr + " has entered evaluate loop");
if (typeof expr === 'string') {
console.log(expr + " is a symbol");
return env.get(expr);
} else if (typeof expr === 'number') {
console.log(expr + " is a number");
return expr;
} else if (expr[0] === 'define') { // (define var value)
console.log(expr + " is a define statement");
var newVar = expr[1];
var newVal = evaluate(expr[2], env);
env.add(newVar, newVal);
return env;
} else if (expr[0] === 'lambda') { // (lambda args body)
console.log(expr + " is a lambda statement");
var args = expr[1];
var body = expr[2];
return createLambda(args, body, env);
} else if (expr[0] === 'quote') {
return expr[1];
} else if (expr[0] === 'cond'){
console.log(expr + " is a conditional");
for (var i = 1; i < expr.length; i++){
var temp = expr[i];
if (evaluate(temp[0], env)) {
console.log(temp[0] + " is evaluated as true");
return evaluate(temp[1], env);
}
}
console.log("no case was evaluated as true");
return;
} else if (expr[0] === 'if') {
console.log(expr + "is an if case");
return function(test, caseyes, caseno, env){
if (test) {
return evaluate(caseyes, env);
} else {
return evaluate(caseno, env);
}
}(evaluate(expr[1], env), expr[2], expr[3], env);
} else if (typeof expr[0] === 'string'){
console.log(expr + " is a function call");
var lispFunc = env.get(expr[0]);
var lispFuncArgs = [];
for(var i = 1; i < expr.length; i++){
lispFuncArgs.push(evaluate(expr[i], env));
}
return lispFunc.apply(this, lispFuncArgs);
} else if (isArray(expr)){
if (expr[0][0] === 'lambda' || expr[0][0] === 'string') {
console.log("This is a special lambda");
var lambdaFunc = evaluate(expr[0], env)
var lambdaArgs= [];
for(var i = 1; i < expr.length; i++){
lambdaArgs.push(expr[i]);
}
return lambdaFunc.apply(this, lambdaArgs);
} else {
console.log(expr + " is a list");
var evaluatedList = [];
for(var i = 0; i < expr.length; i++){
evaluatedList.push(evaluate(expr[i], env));
}
return evaluatedList;
}
} else {
console.log(expr + " cannot be interpreted");
}
}
var globalEnvironment = new environment(null, "Global");
addPrimitives(globalEnvironment);
function start(string) {
return evaluate(parse(string), globalEnvironment);
}
var output = function (string) {
try {
document.getElementById('debugdiv').innerHTML = start(string);
} catch (e) {
document.getElementById('debugdiv').innerHTML = e.name + ': ' + e.message;
}
};
Full HTML;
<html>
<head>
<meta content="text/html; charset=UTF-8" http-equiv="Content-Script-Type" content="text/javascript">
<title>LISP in JavaScript</title>
<script type="text/javascript" src="lisp.js"></script>
</head>
<body>
<form id="repl" name="repl" action="parse(prompt.value)">
lisp==>
<input id="prompt" size="200" value="" name="prompt" maxlength="512">
<br>
<input type=button style="width:60px;height:30px" name="btnEval" value="eval" onclick="output(prompt.value)">
<br>
</form>
<div id="debugdiv" style="background-color:orange;width=100px;height=20px">
</div>
</body>
</html>
Further thoughts, suggestions and comments are of course also welcome.
Thank you!

You don't inspect the structure of the operand to see if it's a lambda you eval the operand. The standard way of eval is to check if it's primitive type, then check for special forms and macros, then eval the operator and operands before applying.
Just remove the part where expr[0][0] === 'lambda' || expr[0][0] === 'string' is true and instead of just returning the evaluation of the form you need to apply the operand:
else if (isArray(expr)){
const fn = evaluate(expr[0], env);
const evaluatedList = [];
for(var i = 1; i < expr.length; i++){
evaluatedList.push(evaluate(expr[i], env));
}
return fn(...evaluatedList);
}
The createLambda is wrong since you are evaluating the arguments in the wrong environment. This would be correct since the arguments are already evaluated:
function createLambda(args, body, env){ // lambda args body
function runLambda(){
const lambdaEnvironment = new environment(env, "lambda environment");
for (let i = 0; i < arguments.length; i++){
lambdaEnvironment.add(args[i], arguments[i]);
}
return evaluate(body, lambdaEnvironment);
}
return runLambda;
}

Getting nested obj value

Given the following obj:
var inputMapping = {
nonNestedItem: "someItem here",
sections: {
general: "Some general section information"
}
};
I'm writing a function to get that data by passing in a string "nonNestedItem" or in the nested case "sections.general". I'm having to use an eval and I was wondering if there was maybe a better way to do this.
Here is what I have so far and it works okay. But improve!
function getNode(name) {
var n = name.split(".");
if (n.length === 1) {
n = name[0];
} else {
var isValid = true,
evalStr = 'inputMapping';
for (var i=0;i<n.length;i++) {
evalStr += '["'+ n[i] +'"]';
if (eval(evalStr) === undefined) {
isValid = false;
break;
}
}
if (isValid) {
// Do something like return the value
}
}
}
Linky to Jsbin

You can use Array.prototype.reduce function like this
var accessString = "sections.general";
console.log(accessString.split(".").reduce(function(previous, current) {
return previous[current];
}, inputMapping));
Output
Some general section information
If your environment doesn't support reduce, you can use this recursive version
function getNestedItem(currentObject, listOfKeys) {
if (listOfKeys.length === 0 || !currentObject) {
return currentObject;
}
return getNestedItem(currentObject[listOfKeys[0]], listOfKeys.slice(1));
}
console.log(getNestedItem(inputMapping, "sections.general".split(".")));

You don't need to use eval() here. You can just use [] to get values from an object. Use a temp object to hold the current value, then update it each time you need the next key.
function getNode(mapping, name) {
var n = name.split(".");
if (n.length === 1) {
return mapping[name];
} else {
var tmp = mapping;
for (var i = 0; i < n.length; i++) {
tmp = tmp[n[i]];
}
return tmp;
}
}

JS: How to return 'undefined' instead of throwing error 'cannot read property x of undefined'

What is the best way to have js return undefined rather than throw an error when a parent property does not exist?
Example
a = {}
b = a.x.y.z
// Error: Cannot read property 'value' of undefined
// Target result: b = undefined

You have to check for the existence of each property:
var b;
if (a.x && a.x.y && a.x.y.z) {
b = a.x.y.z
}
Or, simliar to another poster's "safeGet" function:
var get = function (obj, ns) {
var y = ns.split('.');
for(var i = 0; i < y.length; i += 1) {
if (obj[y[i]]) {
obj = obj[y[i]];
} else {
return;
}
}
return obj;
};
Use:
var b = get(a, 'x.y.z');

try {
a = {}
b = a.x.y.z
}
catch (e) {
b = void 0;
}

I would go for slightly verbose:
var b = ((a.x || {}).y || {}).z

you could write a safeGet helper function, something like:
edited for drilldown as suggested in comments by arcyqwerty
var getter = function (collection, key) {
if (collection.hasOwnProperty(key)) {
return collection[key];
} else {
return undefined;
}
};
var drillDown = function (keys, currentIndex, collection) {
var max = keys.length - 1;
var key = keys[currentIndex];
if (typeof collection === 'undefined') {
return undefined;
}
if (currentIndex === max) {
return getter(collection, key);
} else {
return drillDown(keys, currentIndex + 1,
getter(collection, key));
}
};
var safeGet = function (collection, key) {
if (key.indexOf(".") !== -1) {
return drillDown(key.split("."), 0, collection);
} else {
return getter(collection, key);
}
};
a = { x: 1 };
b = safeGet(a, 'x.y.z');
http://jsfiddle.net/YqdWH/2/

javascript comparing arrays of objects

I'm getting a "Maximum call stack size exceeded." while trying to iterate the contents of an array and I can't for the life of me figure out why
Edit: By the way I want to add that this is for Safari
here's the function:
function compareObj(a,b) {
var u = function(c,d) {//Check types
var type = Object.prototype.toString.call(a)
if (type !== Object.prototype.toString.call(b)) return false
return type.slice(8,-1) == 'Array' ? v(a,b) : type.slice(8,-1) == 'Object' ? w(a,b) :
type.slice(8,-1) == 'String' ? x(a,b) : type.slice(8,-1) == 'Number' ? y(a,b) :
type.slice(8,-1) == 'Boolean' ? z(a,b) : false ;
}
var v = function(c,d) {//Array
if (c.length !== d.length) return false
/*for (var i = 0; i < c.length; i++) {
if (!u(c[i],d[i])) {
return false
}
}*/
while (c.length) {
if (!u(c[0],d[0])) {
return false
} else {
c.shift();
d.shift();
}
}
return true
}
var w = function(c,d) {//Object
for (i in c) {
}
return true
}
var x = function(c,d) {//String
return c === d
}
var y = function(c,d) {//Number
return c === d
}
var z = function(c,d) {//Boolean
return c === d
}
return u(a,b)
}
I get the overload in the return statement of the u() function

Your function can be a lot shorter. It's advisable to use meaningfull function names. Some functions are redundant. There is no need for recursion. I took the liberty to rewrite your function, just for demonstration. You can see it in action here.
function compareObj(a,b) {
var doCompare = function(c,d) {
//Check types (IE compatible)
var objRE = /Array|Object|String|Number|Boolean/,
aType = a.constructor.name || String(a.constructor).match(objRE)[0],
bType = b.constructor.name || String(b.constructor).match(objRE)[0];
//Types different? No dice.
if (aType !== bType) {return false;}
switch(aType){
case 'Array' : return arrayCompare(a,b); break;
case 'Object' : return objectCompare(a,b); break;
case 'String' : return valueCompare(a,b); break;
case 'Number' : return valueCompare(a,b); break;
case 'Boolean': return valueCompare(a,b); break;
default: return false
}
}
var arrayCompare = function(c,d) { //Array
if (c.length !== d.length) {return false;}
var i = c.length;
while (--i) {
if ( !valueCompare(c[i],d[i]) ) {
return false;
}
}
return true;
}
var objectCompare = function(c,d) { //Object
//you'll have to consider the number of elements too
var lenb = 0, lena = 0;
for (var label in d){
if (d.hasOwnProperty(label)) { lenb+=1; }
}
for (var label in c) {
if (c.hasOwnProperty(label)){
lena += 1;
if ( !valueCompare(c[label],d[label]) ) {
return false;
}
}
}
return lena === lenb;
}
var valueCompare = function(c,d) {//String
return JSON.stringify(c) === JSON.stringify(d);
}
return doCompare(a,b);
}
Actually, if you use JSON (native in newer browsers, or from library), you can do all this just using:
function compare(a,b){
return JSON.stringify(a) === JSON.stringify(b);
}