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day2016-template-engine.html
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<!DOCTYPE html>
<html lang="zh">
<head>
<meta charset="UTF-8">
<title>Template Engine</title>
<script src="https://cdn.staticfile.net/jquery/3.7.1/jquery.js"></script>
<style>
body {
max-width: 400px;
background-color: #101010;
color: white;
font-size: 20px;
font-family: Consolas, NSimSun, serif;
}
main#render-target {
outline: solid 2px #ff7200;
}
.notes > .note {
list-style: simp-chinese-informal;
}
</style>
</head>
<body>
<script type="text/x-te-template" id="list-with-title">
<div class="te-list-wrap">
<h2>{{ ctx.title }}</h2>
<ul>
<li>{{ {a:10,b:20} }}</li>
<li>Title's length is {{ {{}} ctx.title.length }}</li>
<li>{{ ctx.title.length > 10 ? 'maybe too long' : 'may be too short' }}</li>
<li>{{@ <div> verbatim-1 </div>}}</li>
<li>{{@ }}{{}} curly braces }}</li>
<li>{{@ verbatim-2 {{ []}} {{ }} }}</li>
<li>}}{{}}</li>
</ul>
{{if 20 > 10}}
<p>This text should be rendered, 20>10 is {{20>10}}</p>
{{/if}}
{{if !(20 > 10)}}
<p>This text should be not rendered, !(20 > 10) is {{!(20 > 10)}}</p>
{{/if}}
{{if 20 > 10}}
{{if 20 > 15}}
<p>20 > 15</p>
{{/if}}
{{if 20 < 15}}
<p>20 < 15</p>
{{/if}}
<p>20>10</p>
{{/if}}
</div>
</script>
<main id="render-target"></main>
<ul class="notes">
<li class="note">统统使用贪心正则，如果表达式求值出错，则视为 {{@ }}</li>
</ul>
<script>
function isObject(value) {
const type = typeof value;
return !!value && (type === "object" || type === "function");
}
</script>
<script>
function renderToText(tpl, ctx) {
const doubleCurlyBraces = /{{(.*)}}/g;
ctx.__conditionalBlockStack = ctx.__conditionalBlockStack ?? [];
return tpl.replaceAll(doubleCurlyBraces, dispatch);
function dispatch(all, inner, index, template) {
function betterEval(expr, ...args) {
return (new Function("ctx", `return (${expr});`))(...args);
}
function emitJsExpr(_, expr) {
let value;
try {
value = betterEval(expr, ctx);
} catch {
return emitVerbatim(_, expr, true);
}
if (isObject(value)) {
const tag = Object.prototype.toString.call(value);
if (tag === "[object Function]") {
return value.toString();
}
return JSON.stringify(value);
}
return value;
}
function emitVerbatim(a, i, mustEmit = false) {
if (mustEmit === true || a.startsWith("{{@")) {
return i.slice(1);
}
return null;
}
function ignoreEmpty(_, i) {
if (i.trim().length === 0) {
return "";
}
return null;
}
function emitConditionalBlock(a, i) {
const isCondStart = a.startsWith("{{if");
const isCondEnd = a.startsWith("{{/if");
if (!isCondStart && !isCondEnd) {
return null;
}
if (isCondStart) {
const booleanExpr = i.slice(2);
const shouldExec = betterEval(booleanExpr);
ctx.__conditionalBlockStack.push(shouldExec);
console.log(`conditional block starts ${booleanExpr} = ${shouldExec}`);
return "";
}
if (isCondEnd) {
ctx.__conditionalBlockStack.pop();
console.log("conditional block ends");
return "";
}
}
const emitters = [
ignoreEmpty,
emitConditionalBlock,
emitVerbatim,
emitJsExpr,
];
for (const echo of emitters) {
const result = echo(all, inner, index, template);
if (result !== null) {
const fnName = echo.toString().match(/function (\w+)/)[1];
console.log(fnName, "echos", `^${result}$`);
return result;
}
}
return "!!error!!";
}
}
const context = {
title: "Title rendered by te",
};
const templateText = $("#list-with-title").text().trim();
const rendered = renderToText(templateText, context);
console.log("rendered\n", rendered);
$("main#render-target").html(rendered);
</script>
</body>
</html>