Today I spent several hours trying to find out why this code does not work:<\/p>\n\n\n\n
function doit() {
return
someObject
.method1()
.method2();
}<\/pre>\n\n\n\nbut this one does:<\/p>\n\n\n\n
function doit() {
let temp;
return temp =
someObject
.method1()
.method2();
}<\/pre>\n\n\n\nIt involved some rather complicated promises and what-not, so I was tossing them around, trying to figure out where it gets stuck. The answer, however, is rather simple: unfortunate code formatting. When return<\/code> is on a line by itself, Javascript inserts an implicit semicolon after it, and completely ignores subsequent code, quietly returning undefined<\/code>:<\/p>\n\n\n\nfunction doit() {
return ;<\/span>
someObject;<\/span>
.method1();<\/span>
.method2();
}<\/pre>\n\n\n\nPorting formatting habits from one language to another may be dangerous: not all whitespace is created equal. It is kind of obvious with Python, but Javascript may be tricky as well.<\/p>\n\n\n\n
Of course, this happened before to other people. There is even a note in some coding conventions<\/a> that reads “The return value expression must start on the same line as the\u00a0<\/em>return<\/em><\/code>\u00a0keyword in order to avoid semicolon insertion<\/em>“. In fact, I knew about the implicit semicolon, but I did not connect the dots, I was too busy debugging my promises \ud83d\ude42<\/p>\n\n\n\nThat’s all folks \ud83d\ude42<\/p>\n","protected":false},"excerpt":{"rendered":"