Use locally generated ideographs
Rendering Chinese/Japanese/Korean (CJK) ideographs and precomposed Hangul Syllables requires downloading large amounts of font data, which can significantly slow map load times. Use the 'localIdeographFontFamily' setting to speed up map load times by using locally available fonts instead of font data fetched from the server. This setting defines a CSS 'font-family' for locally overriding generation of glyphs in the 'CJK Unified Ideographs' and 'Hangul Syllables' Unicode ranges. In these ranges, font settings from the map's style will be ignored in favor of the locally available font. Keywords in the fontstack defined in the map's style (light/regular/medium/bold) will be translated into a CSS 'font-weight'. When using this setting, keep in mind that the fonts you select may not be available on all users' devices. It is best to specify at least one broadly available fallback font class such as 'sans-serif'.
<!DOCTYPE html>
<html>
<head>
    <meta charset='utf-8' />
    <title></title>
    <meta name='viewport' content='initial-scale=1,maximum-scale=1,user-scalable=no' />
    <script src='https://api.tiles.mapbox.com/mapbox-gl-js/v0.39.1/mapbox-gl.js'></script>
    <link href='https://api.tiles.mapbox.com/mapbox-gl-js/v0.39.1/mapbox-gl.css' rel='stylesheet' />
    <style>
        body { margin:0; padding:0; }
        #map { position:absolute; top:0; bottom:0; width:100%; }
    </style>
</head>
<body>

<div id='map'></div>

<script>
mapboxgl.accessToken = '<your access token here>';

var map = new mapboxgl.Map({
    container: 'map',
    style: 'mapbox://styles/mapbox/streets-v9',
    center: [120.3049, 31.4751],
    zoom: 12,
    localIdeographFontFamily: "'Noto Sans', 'Noto Sans CJK SC', sans-serif"
});

</script>

</body>
</html>
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