Template from string

The returned value isn't a random string, but rather the result of a hash function on the parameters. The returned value is 36 characters long. It isn't globally unique. To create a new GUID that isn't based on that hash value of the parameters, use the newGuid function. An integer that represents the position of the item to find. The value is zero-based. If the item isn't found, -1 is returned.

The following example shows how to use the indexOf and lastIndexOf functions:. For more information, see json function. A string of the last character, or the type string, int, array, or object of the last element in an array.

An integer that represents the last position of the item to find. Returns the number of characters in a string, elements in an array, or root-level properties in an object. The following example shows how to use the length function with an array and string:.

Returns a value in the format of a globally unique identifier. This function can only be used in the default value for a parameter. You can only use this function within an expression for the default value of a parameter. Using this function anywhere else in a template returns an error. The function isn't allowed in other parts of the template because it returns a different value each time it's called. Deploying the same template with the same parameters wouldn't reliably produce the same results.

The newGuid function differs from the guid function because it doesn't take any parameters. When you call guid with the same parameter, it returns the same identifier each time. Use guid when you need to reliably generate the same GUID for a specific environment. Use newGuid when you need a different identifier each time, such as deploying resources to a test environment. The newGuid function uses the Guid structure in the.

NET Framework to generate the globally unique identifier. If you use the option to redeploy an earlier successful deployment , and the earlier deployment includes a parameter that uses newGuid, the parameter isn't reevaluated. Instead, the parameter value from the earlier deployment is automatically reused in the rollback deployment. In a test environment, you may need to repeatedly deploy resources that only live for a short time.

Rather than constructing unique names, you can use newGuid with uniqueString to create unique names. I wanted to present an easy solution to the problem and provided a simplified example of what can be done. No, that's exactly what would not work - new Function doesn't have access to the var name in the template function.

The second snip fixed my problem Up vote from me! Thanks, this helped solve a temporary problem we were having with dynamic routing to an iframe : — Kris Boyd. Matt Browne Matt Browne Can you post an example actually using this? This javascript is a bit beyond me. I have a working solution but I'm not sure it's as portable as yours, so I'd love to see how this should be implemented in a page. Mine also uses eval. I went ahead and posted an answer as well, and I'd love your feedback on how to make that more secure and performance-minded: stackoverflow.

RegularJoe I added an example. My goal was to keep it simple, but you're right that if you want to handle nested curly braces, you would need to change the regex. However, I can't think of a use case for that when evaluating a regular string as if it were a template literal the whole purpose of this function. What did you have in mind? Also, I am neither a performance expert nor a security expert; my answer is really just combining two previous answers. But I will say that using eval leaves you a lot more open to possible mistakes that would cause security issues, whereas all my version is doing is looking up a property on an object from a dot-separated path, which should be safe.

I liked s. Daniel Daniel 6, 4 4 gold badges 51 51 silver badges 75 75 bronze badges. Really Neat! Why the reducer? So i wrote down my own solution using regex.

Mohit Pandey Mohit Pandey 3, 7 7 gold badges 23 23 silver badges 38 38 bronze badges. However, rather than try to invent a templating pattern, you are probably better off just using mustache or similar. You can use the string prototype, for example String. I agree, but I think this is one of the very few use cases in which one could say, "mmhkay, let's use it". Please check jsperf.

AndreaPuddu, your performance is indeed better. But then again; template strings are unsupported in IE. The only purpose of that test was to see the potential performance issues using eval. Regarding template literals: thanks for pointing that out again. Robert Moskal Robert Moskal Since we're reinventing the wheel on something that would be a lovely feature in javascript.

Regular Jo Regular Jo 4, 3 3 gold badges 19 19 silver badges 36 36 bronze badges. Sign up or log in Sign up using Google. Sign up using Facebook. Sign up using Email and Password. Post as a guest Name. Email Required, but never shown. The Overflow Blog. Stack Gives Back Safety in numbers: crowdsourcing data on nefarious IP addresses. This allows us to modify the regular expression patterns and other attributes of the class to meet our specific needs.

In this section, we'll be covering how to customize some of the most important attributes of the class and how this impact the general behavior of our Template objects. Let's start with the class attribute. The class attribute delimiter holds the character used as the placeholder's starting character.

Since the Python Template class is designed for inheritance, we can subclass Template and change the default value of delimiter by overriding it. We can use our MyTemplate class just like we use the regular Python Template class. This can be handy when we're working with strings that handle a lot of dollar signs, for example, when we're dealing with currencies.

Note : Do not replace a delimiter with a regular expression. The template class automatically escapes the delimiter. Therefore, if we use a regular expression as delimiter it's highly likely that our custom Template would not work correctly. The idpattern class attribute holds a regular expression that is used to validate the second half of a placeholder in a template string. In other words, idpattern validates that the identifiers we use in our placeholders are valid Python identifiers.

The default value of idpattern is r'? We can subclass Template and use our own regular expression pattern for idpattern. To do this, we can override idpattern and remove these characters from the pattern as follow:.

That's why we get a KeyError in each case. There could be situations where we need to modify the behavior of the Python Template class, but overriding delimiter , idpattern , or both is not enough. In these cases, we can go further and override the pattern class attribute to define an entirely new regular expression for our custom Template subclasses. If you decide to use a whole new regular expression for pattern , then you need to provide a regular expression with four named groups:.

The pattern property holds a compiled regular expression object. However, it's possible to inspect the original regular expression string by accessing the pattern attribute of the pattern property.

Check out the following code:. This code outputs the default string used to compile the pattern class attribute. In this case, we can clearly see the four named groups that conform to the default regular expression.

As stated before, if we need to deeply customize the behavior of Template , then we should provide these same four named groups along with specific regular expressions for each group. Note: The built-in functions eval and exec can have important security implications when used with malicious input.

Use with caution! The special raw property, available on the first argument to the tag function, allows you to access the raw strings as they were entered, without processing escape sequences. In addition, the String. This means that a tagged template like the following is problematic, because, per ECMAScript grammar, a parser looks for valid Unicode escape sequences, but finds malformed syntax:.

Tagged templates should allow the embedding of languages for example DSLs , or LaTeX , where other escapes sequences are common. Note that the escape sequence restriction is only dropped from tagged templates—not from untagged template literals:. Untagged template literals result in strings, which makes them useful for string interpolation and multiline strings, since unescaped newlines are allowed. Tagged template literals call a function the tag function with an array of any text segments from the literal followed by arguments with the values of any substitutions, which is useful for DSLs.

Any newline characters inserted in the source are part of the template literal.