JSON Object with keys and value object

Let us first look at our json object that needs to be iterated. Pretty printing the json file with strigify.

JSON.stringify(obj, null, 2); // spacing level = 2

{
  "Sy": {"speed": 1.0054454,"rashi": 7 },
  "Ch": {"speed": 12.6783487,"rashi": 7 },
  "Ma": {"speed": 0.1587292,"rashi": 12 },
  "Bu": {"speed": 1.5975625,"rashi": 7 },
  "Gu": {"speed": -0.1278241,"rashi": 2 },
  "Sk": {"speed": 1.2191773,"rashi": 6 },
  "Sa": {"speed": 0.097599,"rashi": 9 },
  "Ra": {"speed": -0.0529538,"rashi": 11 },
  "Ke": {"speed": -0.0529538,"degree": 16.842893500000002 }
}

The above js object contains keys and the value are objects too.

Using loops

The usual way of accessign the object is using the traditional for loop

for(var g in obj){
    console.log(g)
}

Using forEach

Instead we can use foreach function.But before we can apply forEach function, we must make the json enumerable using Object.keys()

Object.keys(obj).forEach((k,v)=>{ 
    console.log(v)
})

Reduce function

Group an array of objects by key.

• We are using a property in the value of the object map.
• assigning property value as key value
• grouping keys as values

In the below code, current value is an array with 2 values. e.g. ['Sy', {rashi: 7, speed: 1.0054454}]

Object.entries(obj).reduce(function (totalValues, currentValue) {
        totalValues[currentValue[1].rashi] = totalValues[currentValue[1].rashi] || [];
        totalValues[parseInt(currentValue[1].rashi)].push(currentValue[0]);
        return totalValues;
}, Object.create(null));

will result in following

temp1 = {
  2: ["Gu"],
  5: ["Ke"],
  6: ["Sk"],
  7: ["Sy","Ch","Bu"],
  9: ["Sa"],
  11: ["Ra"],
  12: ["Ma"]
}

In the below line, every item is pushed as value

        totalValues[parseInt(currentValue[1].rashi)].push(currentValue[0]);

We have parsed into an integer for futher computation.

If we add console.log(totalValues), we can observe how totalValues is getting populated.

Convert object to map

map = new Map(Object.entries(temp1))

Check key in a map

if(key in temp1){ // key i in map
   // key is available in map
}  

Array to string

With join method you can convert array into comma separated string

temp1["7"].join(", ")

NodeList forEach

If we wish to add the data on a nodelist, we can iterate over the nodelist using forEach

const houseNodes = document.getElementById('houses').querySelectorAll('p');
houseNodes.forEach(function(houseNode, i){
    houseNode.innerHTML= "House No "+i;    
})

Rotate an array

We can extend Array with a custom function for rotating the array.

Array.prototype.rotate = function(n) {
    n = n % this.length;
    while (this.length && n < 0) n += this.length;
    this.push.apply(this, this.splice(0, n));
    return this;
}

[...map].rotate(5);

Combine Arrays into a single array

Every array has a concat method that can accept another array and produce the combined array. We can reassign this combined array to original array or assign it to a new array.

combined = arr1.concat(arr2)