模板编译
<body>
<div id="app">
<span>{{ 1 | test(8) }}</span>
</div>
</body>
<script src="./vue.js"></script>
<script>
new Vue({
el: "#app",
filters: {
test (val, b) {
console.log(this)
debugger
return val + b
}
}
});
模板在编译成render函数时候会经过下面一系列流程：
parseText
主要在parseText函数解析文本
function parseText (
text,
delimiters
) {
debugger
var tagRE = delimiters ? buildRegex(delimiters) : defaultTagRE;
if (!tagRE.test(text)) {
return
}
var tokens = [];
var rawTokens = [];
var lastIndex = tagRE.lastIndex = 0;
var match, index, tokenValue;
while ((match = tagRE.exec(text))) {
index = match.index;
// push text token
if (index > lastIndex) {
rawTokens.push(tokenValue = text.slice(lastIndex, index));
tokens.push(JSON.stringify(tokenValue));
}
// tag token
var exp = parseFilters(match[1].trim());
tokens.push(("_s(" + exp + ")"));
rawTokens.push({ '@binding': exp });
lastIndex = index + match[0].length;
}
if (lastIndex < text.length) {
rawTokens.push(tokenValue = text.slice(lastIndex));
tokens.push(JSON.stringify(tokenValue));
}
return {
expression: tokens.join('+'),
tokens: rawTokens // 解析成 ["_s(_f("test")(1,8))"]
}
}
_f函数就是resolveFilter函数
function resolveFilter (id) {
debugger
return resolveAsset(this.$options, 'filters', id, true) || identity
}
function resolveAsset (
options,
type,
id,
warnMissing
) {
/* istanbul ignore if */
if (typeof id !== 'string') {
return
}
var assets = options[type];
// check local registration variations first
if (hasOwn(assets, id)) { return assets[id] }
var camelizedId = camelize(id);
if (hasOwn(assets, camelizedId)) { return assets[camelizedId] }
var PascalCaseId = capitalize(camelizedId);
if (hasOwn(assets, PascalCaseId)) { return assets[PascalCaseId] }
// fallback to prototype chain
var res = assets[id] || assets[camelizedId] || assets[PascalCaseId];
if (warnMissing && !res) {
warn(
'Failed to resolve ' + type.slice(0, -1) + ': ' + id,
options
);
}
return res
}
resolveAsset就是取出我们在组件中定义在filters里面的test函数,由此可见当我们在定义filter函数中this是不指向当前组件实例的，指向window。如果要想拿到组件实例，可通过调用过滤器的时候，传入this
最终生成的render函数