JavaScript返回语句错误

Question

This is my original code it is a cache using jquery deferreds/promises

var templateCache = {};

var retrieve = function (templateURL) {
    if (!templateCache[templateURL]) {
        templateCache[templateURL] = $.get(templateURL);
    }
    return templateCache[templateURL];
};

I wanted to try to change it to a one liner so i made

var templateCache = {};
var retrieve = function( templateURL ){
  return templateCache[ templateURL ] || templateCache[ templateURL ] = $.get( templateURL );
}

But I keep getting an error that the left hand side of the return statement is invalid

Answer 1

在作业周围添加一些括号

return templateCache[ templateURL ] || (templateCache[ templateURL ] = $.get( templateURL ));

Answer 2

|| has a higher precedence than = .

Your code is being parsed as (a || b) = c , which doesn't make any sense.

You need to add parentheses to force the assignment to happen first:

a || (b = c)

Answer 3

here is another way to write it using a ternary operator.

var retrieve = function( templateURL ){
    return templateCache[ templateURL ] ? templateCache[ templateURL ] : templateCache[ templateURL ] = $.get( templateURL );
};