I'm trying to do something like the following in React JSX (where ObjectRow is a separate component):
<tbody>
for (var i=0; i < numrows; i++) {
<ObjectRow/>
}
</tbody>
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).
78 Answers
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++) {
ObjectRow()
}
)
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++) {
rows.push(ObjectRow());
}
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.
I am not sure if this will work for your situation, but often map is a good answer.
If this was your code with the for loop:
<tbody>
for (var i=0; i < objects.length; i++) {
<ObjectRow obj={objects[i]} key={i}>
}
</tbody>
You could write it like this with map:
<tbody>
{objects.map(function(object, i){
return <ObjectRow obj={object} key={i} />;
})}
</tbody>
ES6 syntax:
<tbody>
{objects.map((object, i) => <ObjectRow obj={object} key={i} />)}
</tbody>
If you don't already have an array to map() like @FakeRainBrigand's answer, and want to inline this so the source layout corresponds to the output closer than @SophieAlpert's answer:
With ES2015 (ES6) syntax (spread and arrow functions)
<tbody>
{[...Array(10)].map((x, i) =>
<ObjectRow key={i} />
)}
</tbody>
Re: transpiling with Babel, its caveats page says that Array.from is required for spread, but at present (v5.8.23) that does not seem to be the case when spreading an actual Array. I have a documentation issue open to clarify that. But use at your own risk or polyfill.
Vanilla ES5
Array.apply
<tbody>
{Array.apply(0, Array(10)).map(function (x, i) {
return <ObjectRow key={i} />;
})}
</tbody>
