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@axetroy /index.js
Last active Mar 9, 2018

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basic-vm
const babylon = require("babylon");
const types = require("babel-types");
const visitors = {
File(node, scope) {
evaluate(node.program, scope);
},
Program(program, scope) {
for (const node of program.body) {
evaluate(node, scope);
}
},
ExpressionStatement(node, scope) {
return evaluate(node.expression, scope);
},
CallExpression(node, scope) {
// 获取调用者对象
const func = evaluate(node.callee, scope);
// 获取函数的参数
const funcArguments = node.arguments.map(arg => evaluate(arg, scope));
// 如果是获取属性的话: console.log
if (types.isMemberExpression(node.callee)) {
const object = evaluate(node.callee.object, scope);
return func.apply(object, funcArguments);
} else if (types.isIdentifier(node.callee)) {
func.apply(scope, funcArguments);
}
},
MemberExpression(node, scope) {
const {object, property} = node;
// 找到对应的属性名
const propertyName = property.name;
// 找对对应的对象
const obj = evaluate(object, scope);
// 获取对应的值
const target = obj[propertyName];
// 返回这个值,如果这个值是function的话,那么应该绑定上下文this
return typeof target === "function" ? target.bind(obj) : target;
},
Identifier(node, scope) {
// 获取变量的值
return scope[node.name];
},
StringLiteral(node) {
return node.value;
},
NumericLiteral(node) {
return node.value;
},
VariableDeclaration(node, scope) {
const kind = node.kind;
for (const declartor of node.declarations) {
const {name} = declartor.id;
const value = declartor.init
? evaluate(declartor.init, scope)
: undefined;
scope[name] = value;
}
},
VariableDeclarator(node, scope) {
scope[node.id.name] = evaluate(node.init, scope);
},
BlockStatement(block, scope) {
for (const node of block.body) {
// 执行代码块中的内容
evaluate(node, scope);
}
},
FunctionDeclaration(node, scope) {
// 获取function
const func = visitors.FunctionExpression(node, scope);
// 在作用域中定义function
scope[node.id.name] = func;
},
FunctionExpression(node, scope) {
// 自己构造一个function
const func = function() {
// TODO: 获取函数的参数
// 执行代码块中的内容
evaluate(node.body, scope);
};
// 返回这个function
return func;
}
};
function evaluate(node, scope) {
const _evalute = visitors[node.type];
if (!_evalute) {
throw new Error(`Unknown visitors of ${node.type}`);
}
// 递归调用
return _evalute(node, scope);
}
const code = `
function test(){
var name = "hello world";
console.log(name);
}
test();
`;
// 生成AST树
const ast = babylon.parse(code);
// 解析AST
// 需要传入执行上下文,否则找不到``console``对象
evaluate(ast, {console, Math});
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