packages/babel-plugin-transform-template-literals/src/index.js
import { declare } from "@babel/helper-plugin-utils";
import { template, types as t } from "@babel/core";
export default declare((api, options) => {
api.assertVersion(7);
const { loose } = options;
let helperName = "taggedTemplateLiteral";
if (loose) helperName += "Loose";
/**
* This function groups the objects into multiple calls to `.concat()` in
* order to preserve execution order of the primitive conversion, e.g.
*
* "".concat(obj.foo, "foo", obj2.foo, "foo2")
*
* would evaluate both member expressions _first_ then, `concat` will
* convert each one to a primitive, whereas
*
* "".concat(obj.foo, "foo").concat(obj2.foo, "foo2")
*
* would evaluate the member, then convert it to a primitive, then evaluate
* the second member and convert that one, which reflects the spec behavior
* of template literals.
*/
function buildConcatCallExpressions(items) {
let avail = true;
return items.reduce(function (left, right) {
let canBeInserted = t.isLiteral(right);
if (!canBeInserted && avail) {
canBeInserted = true;
avail = false;
}
if (canBeInserted && t.isCallExpression(left)) {
left.arguments.push(right);
return left;
}
return t.callExpression(
t.memberExpression(left, t.identifier("concat")),
[right],
);
});
}
return {
name: "transform-template-literals",
visitor: {
TaggedTemplateExpression(path) {
const { node } = path;
const { quasi } = node;
const strings = [];
const raws = [];
// Flag variable to check if contents of strings and raw are equal
let isStringsRawEqual = true;
for (const elem of (quasi.quasis: Array)) {
const { raw, cooked } = elem.value;
const value =
cooked == null
? path.scope.buildUndefinedNode()
: t.stringLiteral(cooked);
strings.push(value);
raws.push(t.stringLiteral(raw));
if (raw !== cooked) {
// false even if one of raw and cooked are not equal
isStringsRawEqual = false;
}
}
const scope = path.scope.getProgramParent();
const templateObject = scope.generateUidIdentifier("templateObject");
const helperId = this.addHelper(helperName);
const callExpressionInput = [t.arrayExpression(strings)];
// only add raw arrayExpression if there is any difference between raws and strings
if (!isStringsRawEqual) {
callExpressionInput.push(t.arrayExpression(raws));
}
const lazyLoad = template.ast`
function ${templateObject}() {
const data = ${t.callExpression(helperId, callExpressionInput)};
${templateObject} = function() { return data };
return data;
}
`;
scope.path.unshiftContainer("body", lazyLoad);
path.replaceWith(
t.callExpression(node.tag, [
t.callExpression(t.cloneNode(templateObject), []),
...quasi.expressions,
]),
);
},
TemplateLiteral(path) {
const nodes = [];
const expressions = path.get("expressions");
let index = 0;
for (const elem of (path.node.quasis: Array)) {
if (elem.value.cooked) {
nodes.push(t.stringLiteral(elem.value.cooked));
}
if (index < expressions.length) {
const expr = expressions[index++];
const node = expr.node;
if (!t.isStringLiteral(node, { value: "" })) {
nodes.push(node);
}
}
}
// since `+` is left-to-right associative
// ensure the first node is a string if first/second isn't
const considerSecondNode = !loose || !t.isStringLiteral(nodes[1]);
if (!t.isStringLiteral(nodes[0]) && considerSecondNode) {
nodes.unshift(t.stringLiteral(""));
}
let root = nodes[0];
if (loose) {
for (let i = 1; i < nodes.length; i++) {
root = t.binaryExpression("+", root, nodes[i]);
}
} else if (nodes.length > 1) {
root = buildConcatCallExpressions(nodes);
}
path.replaceWith(root);
},
},
};
});