performance - JavaScript object property assignment -


on page -> https://developer.mozilla.org/en-us/docs/web/javascript/a_re-introduction_to_javascript

" once created, object's properties can again accessed in 1 of 2 ways:

obj.name = "simon"; var name = obj.name;  obj["name"] = "simon"; var name = obj["name"];

these semantically equivalent. the second method has advantage name of property provided string, means can calculated @ run-time though using method prevents javascript engine , minifier optimizations being applied."

(in bold) why second method better? javascript , minifier optimizations referred here?

please let me know if need more information

the second not 'better' safer, allows properties unconventional characters. example:

obj.my-property = true; //parse errror obj['my-property'] = true; //fine, because property name specified string

it allows build dynamic property names, e.g.

var prop_name = 'foo'; prop_name += 'bar'; obj[prop_name] = true;

the optimisation/minification point has fact if not minifiers leave strings strictly untouched, reasons obvious. had:

var str = "hello";

even if minified script, want string stay "hello".

so minification engine may turn

obj.foobar = true;

into

a.b=true;

but wouldn't change

obj['foobar'] = true;

into

a['b']=true;

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