compression and replacing vars/consts

test-const-result.js

//arian@arian-sys:~/www/wrapup (master) $ ./node_modules/.bin/uglifyjs test.js --compress --mangle --define ES5=false
//WARN: Condition always true [test.js:6,34]
//WARN: Dropping unreachable code [test.js:9,2]
function foo(){console.log("es5")}

test-const.js

function foo(){

  const ES5 = true

	if (typeof ES5 != 'undefined' && ES5)
		console.log('es5')
	else
		console.log('not es5')

}

test-var-result.js

// arian@arian-sys:~/www/wrapup (master) $ ./node_modules/.bin/uglifyjs test.js --compress --mangle --define ES5=false
function foo(){var o=!0;o!==void 0&&o?console.log("es5"):console.log("not es5")}

test-var.js

function foo(){

  var ES5 = true

	if (typeof ES5 != 'undefined' && ES5)
		console.log('es5')
	else
		console.log('not es5')

}