I have the following code (snippet out of a larger program and within an async function):
foo = questionData.media ? (await new Promise(resolve => {
const image = new Image();
image.onload = function () {
const canvas = document.ceateElement("canvas");
canvas.width = this.width;
canvas.height = this.height;
canvas.drawImage(image, 0, 0, this.width, this.height);
resolve(canvas.toDataURL("image/jpg"));
};
image.src = "https://example.com/" + questionData.media;
})) : false;
I keep getting SyntaxError: Unexpected token 'new' on the first line, and I have no idea why. When I try to use parenthesis:
foo = questionData.media ? (await (new Promise(resolve => {
const image = new Image();
image.onload = function () {
const canvas = document.ceateElement("canvas");
canvas.width = this.width;
canvas.height = this.height;
canvas.drawImage(image, 0, 0, this.width, this.height);
resolve(canvas.toDataURL("image/jpg"));
};
image.src = "https://example.com/" + questionData.media;
}))) : false;
And I get Uncaught ReferenceError: await is not defined.
Meanwhile, I have this code that works just fine:
data.push(await new Promise(resolve => {
const req = new XMLHttpRequest();
req.onreadystatechange = function () {
if (this.readyState === 4 && this.status === 200) {
resolve(this.responseText);
}
};
req.open("GET", `https://example.com/${id}/answer`, true);
req.send();
}));
What am I missing?
It sounds like you aren't in an async function, so await does not get interpreted as a keyword, but as a variable name. If you put the entire initial snippet into an async function, it'll work as expected.
What's going on with
Unexpected token 'new'
and
await is not defined
is that, when you're not in an async function, those words are interpreted as normal identifiers (variable names) - if you switch them out for another placeholder variable name, it makes more sense for why the syntax would be invalid:
foo = questionData.media ? (someVariable new Promise(resolve => {
foo = questionData.media ? (someVariable (new Promise(resolve => {
Neither of those makes sense, and so the parser will give you errors as expected, when you use await when not in an async function.