Javascript – Loop inside React JSX


I'm trying to do something like the following in React JSX (where ObjectRow is a separate component):

    for (var i=0; i < numrows; i++) {

I realize and understand why this isn't valid JSX, since JSX maps to function calls. However, coming from template land and being new to JSX, I am unsure how I would achieve the above (adding a component multiple times).

Best Solution

Think of it like you're just calling JavaScript functions. You can't use a for loop where the arguments to a function call would go:

return tbody(
    for (var i = 0; i < numrows; i++) {

See how the function tbody is being passed a for loop as an argument – leading to a syntax error.

But you can make an array, and then pass that in as an argument:

var rows = [];
for (var i = 0; i < numrows; i++) {
return tbody(rows);

You can basically use the same structure when working with JSX:

var rows = [];
for (var i = 0; i < numrows; i++) {
    // note: we are adding a key prop here to allow react to uniquely identify each
    // element in this array. see:
    rows.push(<ObjectRow key={i} />);
return <tbody>{rows}</tbody>;

Incidentally, my JavaScript example is almost exactly what that example of JSX transforms into. Play around with Babel REPL to get a feel for how JSX works.