I am in the process of implementing a filterable list with React. The structure of the list is as shown in the image below.
PREMISE
Here's a description of how it is supposed to work:
- The state resides in the highest level component, the
Search component.
- The state is described as follows:
{
visible : boolean,
files : array,
filtered : array,
query : string,
currentlySelectedIndex : integer
}
files is a potentially very large, array containing file paths (10000 entries is a plausible number).filtered is the filtered array after the user types at least 2 characters. I know it's derivative data and as such an argument could be made about storing it in the state but it is needed forcurrentlySelectedIndex which is the index of the currently selected element from the filtered list.
User types more than 2 letters into the Input component, the array is filtered and for each entry in the filtered array a Result component is rendered
Each Result component is displaying the full path that partially matched the query, and the partial match part of the path is highlighted. For example the DOM of a Result component, if the user had typed 'le' would be something like this :
<li>this/is/a/fi<strong>le</strong>/path</li>
- If the user presses the up or down keys while the
Input component is focused the currentlySelectedIndex changes based on the filtered array. This causes the Result component that matches the index to be marked as selected causing a re-render
PROBLEM
Initially I tested this with a small enough array of files, using the development version of React, and all worked fine.
The problem appeared when I had to deal with a files array as big as 10000 entries. Typing 2 letters in the Input would generate a big list and when I pressed the up and down keys to navigate it it would be very laggy.
At first I did not have a defined component for the Result elements and I was merely making the list on the fly, on each render of the Search component, as such:
results = this.state.filtered.map(function(file, index) {
var start, end, matchIndex, match = this.state.query;
matchIndex = file.indexOf(match);
start = file.slice(0, matchIndex);
end = file.slice(matchIndex + match.length);
return (
<li onClick={this.handleListClick}
data-path={file}
className={(index === this.state.currentlySelected) ? "valid selected" : "valid"}
key={file} >
{start}
<span className="marked">{match}</span>
{end}
</li>
);
}.bind(this));
As you can tell, every time the currentlySelectedIndex changed, it would cause a re-render and the list would be re-created each time. I thought that since I had set a key value on each li element React would avoid re-rendering every other li element that did not have its className change, but apparently it wasn't so.
I ended up defining a class for the Result elements, where it explicitly checks whether each Result element should re-render based on whether it was previously selected and based on the current user input :
var ResultItem = React.createClass({
shouldComponentUpdate : function(nextProps) {
if (nextProps.match !== this.props.match) {
return true;
} else {
return (nextProps.selected !== this.props.selected);
}
},
render : function() {
return (
<li onClick={this.props.handleListClick}
data-path={this.props.file}
className={
(this.props.selected) ? "valid selected" : "valid"
}
key={this.props.file} >
{this.props.children}
</li>
);
}
});
And the list is now created as such:
results = this.state.filtered.map(function(file, index) {
var start, end, matchIndex, match = this.state.query, selected;
matchIndex = file.indexOf(match);
start = file.slice(0, matchIndex);
end = file.slice(matchIndex + match.length);
selected = (index === this.state.currentlySelected) ? true : false
return (
<ResultItem handleClick={this.handleListClick}
data-path={file}
selected={selected}
key={file}
match={match} >
{start}
<span className="marked">{match}</span>
{end}
</ResultItem>
);
}.bind(this));
}
This made performance slightly better, but it's still not good enough. Thing is when I tested on the production version of React things worked buttery smooth, no lag at all.
BOTTOMLINE
Is such a noticeable discrepancy between development and production versions of React normal?
Am I understanding/doing something wrong when I think about how React manages the list?
UPDATE 14-11-2016
I have found this presentation of Michael Jackson, where he tackles an issue very similar to this one: https://youtu.be/7S8v8jfLb1Q?t=26m2s
The solution is very similar to the one proposed by AskarovBeknar's answer, below
UPDATE 14-4-2018
Since this is apparently a popular question and things have progressed since the original question was asked, while I do encourage you to watch the video linked above, in order to get a grasp of a virtual layout, I also encourage you to use the React Virtualized library if you do not want to re-invent the wheel.
See Question&Answers more detail:
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