evanw/esbuild · error · Error

Should be array of strings

Error message

Should be array of strings

What it means

Thrown by read_string() in scripts/uglify-tests.js:391. When a string field's value is an array literal, each element must be an AST_String; a non-string element triggers this error. The array elements are joined with newlines to form a single multi-line string.

Source

Thrown at scripts/uglify-tests.js:391

  function croak(node) {
    throw new Error(tmpl("Can't understand test file {file} [{line},{col}]\n{code}", {
      file: file,
      line: node.start.line,
      col: node.start.col,
      code: make_code(node, { beautify: false })
    }));
  }

  function read_string(stat) {
    if (stat.TYPE == "SimpleStatement") {
      var body = stat.body;
      switch (body.TYPE) {
        case "String":
          return body.value;
        case "Array":
          return body.elements.map(function (element) {
            if (element.TYPE !== "String")
              throw new Error("Should be array of strings");
            return element.value;
          }).join("\n");
      }
    }
    throw new Error("Should be string or array of strings");
  }

  function get_one_test(name, block) {
    var test = { name: name, options: {} };
    var tw = new U.TreeWalker(function (node, descend) {
      if (node instanceof U.AST_Assign) {
        if (!(node.left instanceof U.AST_SymbolRef)) {
          croak(node);
        }
        var name = node.left.name;
        test[name] = evaluate(node.right);
        return true;
      }

View on GitHub (pinned to f6058f8364)

Solutions

1. Ensure every array element is a quoted string literal.
2. Concatenate manually or use a single multi-line string if a non-string value is genuinely needed.

Example fix

// before
expect: ["var a = 1;", 2];

// after
expect: ["var a = 1;", "2"];

function allElementsAreStrings(arrNode) {
  return arrNode instanceof U.AST_Array &&
    arrNode.elements.every(el => el instanceof U.AST_String);
}

const isStringArray = (node) =>
  node instanceof U.AST_Array && node.elements.every(el => el.TYPE === 'String');

try { read_string(stat); }
catch (e) {
  if (/Should be array of strings/.test(e.message)) console.error('Every array element must be a string literal');
  throw e;
}

When it happens

Trigger: Writing `expect: ["a", 1, "b"];` or `expect: ["a", x];` in an uglify test file. Only string literals are permitted inside such arrays.

Common situations: Contributor splits a long expected-output string across lines and accidentally includes a number or identifier in the array.

Related errors

• Should be array of strings
• Duplicated test name "${name}" in ${file}
• Should be string or array of strings
• Unsupported input syntax
• Should be boolean

AI-assisted analysis of evanw/esbuild@f6058f8364 (2026-08-09). Data as JSON: /api/errors/b5757ad4423630f1. Report an issue: GitHub.