javascript - Declaring new variables or using references in functions? -

when defining methods class, better use members or assigning them new variable make faster? imagine, instance in javascript following method:

square: function() {     var x = this.x;     x *= x;     return x; } 

or

square: function() {     this.x *= this.x;     return this.x; } 

in general, difference in speed negligible, meaning premature optimization, should avoided in favor of using whatever method more maintainable.

however, in particular case there major difference in functionality between 2 square methods, shown below.

var = {      x: 2,      square: function() {          var x = this.x;          x *= x;          return x;      }  }    console.log('result of a.square():', a.square()); //output 4  console.log('after square, a.x is:', a.x); //output 2    var b = {      x: 2,      square: function() {          this.x *= this.x;          return this.x;      }  }    console.log('result of b.square():', b.square()); //output 4    //the difference here: b.x 4 while a.x still 2  console.log('after square, b.x is:', b.x); //output 4

the first square method not update this.x, second method will. use whichever version matches intent. simplified versions of each method below, after eliminating premature optimization. gain in maintainability clear.

first version (does not update this.x):

square: function() {     return this.x * this.x; } 

second version (does update this.x):

square: function() {     return this.x *= this.x; }