Tag: es5 features

Major features introduced in ECMAScript 5

1. 1. It’s okay to have trailing commas in object literals. Since beginning javascript allowed trailing commas in the array.

      var obj = { 'name': 'Commands Tech', 'category': 'tech new', }

      However, using trailing commas in JSON is invalid and throws the error.

      var myJSON = '{"name":"CommandsTech", "city":"New York",}';
      
      JSON.parse(myJSON);
      VM793:1 Uncaught SyntaxError: Unexpected token } in JSON at position 42
      at JSON.parse (<anonymous>)
      at <anonymous>:2:6

   2. No reserved keywords for variable names.  Reserved keywords should not be used as variable names. Example:

      var NaN = 'CommandsTech';
      console.log(NaN); // NaN

   3. parseInt() defaults to radix 10
      

   4. JSON.parse() & JSON.stringify()

      JSON.parse(): To convert text into a javascript object
      JSON.stringify(): To convert a javascript object into string

   5. bind()

      Description:  Bind method allows us to call a function with this set explicit. bind method returns a bounded function with the bound object.

      this.x = 10;
      var moduleX = {
      	x : 20,
      	getX: function() { return this.x; }
      }
      var retriveX = moduleX.getX;
      retriveX();
      var getBoundX = retriveX.bind(moduleX);
      getBoundX();
      Output: 20

   6. trim()

      Description: Removes whitespace on both ends of the string and returns a string

      var name = ' commandsTech ';
      name.trim();
      "commandsTech"

   7.  every()

      Description: method takes a function as input parameter and checks if each element in an array passes the test and return a boolean

      var bills = [132, 233, 916, 140];
      function checkBills(bill) {
      return bill >= 100;
      }
      bills.every(checkBills); // Output true

   8.  filter()

      Description:  method creates a new array with all elements that pass a test implemented by the provided function

   9. map()

      Description:  method creates a new array with the result of calling a provided function on each element. 

1. forEach()

   Description: method calling a provided function on every array element.

2. reduce()

   Description: reduce method results in a single value that is a result of calling a reducer function on each element.
   filter, map, forEach, map method examples

3. Date.now()

   Description:  returns the current time

4. Date.prototype.toISOString

5. new Date(string) and Date.parse(string)

6. Object.keys()

   
   
   
   
   Description: Fetch all the keys() present in an object. Object.keys() method returns an array of own properties
   

   const profile = {
   name: 'commandsTech',
   location: 'Hyd',
   };
   console.log(Object.keys(profile)); // ['nane','location']

7. Object.create()
   Description: Create a new object taking the existing object’s prototype

   var profile = {
   name: 'commandsTech'
   }
   var profile2 = Object.create(profile);
   profile2.name; // output: "commandsTech"

8. Object.defineProperty & Object.defineProperties
   Description: Using defineProperties we can modify or define properties on an object.

   const profile = {};
   Object.defineProperties(profile, {
   name: {
   value: 'commandsTech',
   writable: true
   }
   });
   console.log(profile.name);
   // expected output: commandsTech

9. Object.getOwnPropertyDescriptor()
   

   Descriptor: Using this method we can know the description of the property specified within the object

   var profile = {
   name:"ct",
   location: "hyd"
   }
   var descriptor = Object.getOwnPropertyDescriptor(profile, 'name');
   console.log(descriptor.configurable); // output: true

10. Object.getOwnPropertyNames(obj)
    

    Description: All the properties present on an object are returned

    var profile = {
    name:"ct",
    location: "hyd"
    }
    Object.getOwnPropertyNames(profile); // output ['name', 'location']

11. Object.seal()
    

    Description: the seal on object prevents adding of new properties and marks all existing as non-configurable properties. Values of a property can be changed(if writable).

    const profile = {
    name: 'commandsTech'
    };
    Object.seal(profile);

12. Object.freeze()
    

    Description: Object that is frozen cannot be changed. The freeze prevents adding new property & deleting the existing property. Prevents changing the enumerability, configurability or writability or changing. Changing of the prototype is also prevented on the frozen object.

    const profile = {
    name: 'commandsTech'
    };
    Object.freeze(profile);

13. Object.isSealed()
    

    Description: Checks if an object is sealed or not
    

    const profile = {
    name: 'commandsTech'
    };
    console.log(Object.isSealed(profile)); //output: false
    Object.seal(profile);
    console.log(Object.isSealed(profile)); // output: true

14. Object.isFrozen()
    Description: Checks if an object is frozen or not
    

    const profile = {
    name: 'commandsTech'
    };
    console.log(Object.isFrozen(profile)); //output: false
    Object.freeze(profile);
    console.log(Object.isFrozen(profile)); // output: true

15.  Property Attributes: writeable, value, enumerable, configurable, get, set.

16. ‘use strict’;

    Description: Use strict indicates that javascript code should be executed in “strict mode”.

    Example with use strict

    <script>
    "use strict";
    name = 'commandsTech'; // This will throws an error (name is not defined).
    </script>

    Example without use strict

    <script>
    name = 'commandsTech'; // This will not throw an error even though name is not defined
    </script>